Sīmantonnayanaṃ is the third saṃskāra that is to be performed when the wife is pregnant. the apt time for this saṃskāra is from fourth month of pregnancy till the delivery of the child. If due to any unknown or accidental reasons if premature delivery of the child occurs, it is instructed to perform the saṃskāra having the child in the lap. 
Sīmā means parting of the hair on the head. Antaṃ means the end. The main ritual of the saṃskāra is the husband takes a porcupine thorn bound with fig fruits by darbha and touches the wife with that from the navel till the end of the parting of the hair on the head. This is called as sīmantaṃ unnayanaṃ.
Jātakarma is the fourth saṃskāra to be performed right after the birth of the child. As the meaning of the saṃskāra itself is the ritual that is to be performed after birth. 
Right after learning the birth of the child, the father is instructed to bath with the clothes which he is wearing at the time of the news arrival. This kind of bath is known as 'sachēla snānam / naimittika snānam'.  
The main ritual in this saṃskāra is to feed the baby a mixture of cow ghee and honey. The both ingredients are to be mixed with a piece of gold (like ring etc.). The quantity is instructed 'not to be of same proportions'. That is either honey or cow ghee should be in greater quantity than the other. This mixture is to be fed to the child before first breast feed. 
This ritual is instructed to be done before cutting the umbilical cord. Because after cutting the umbilical cord the parents and the paternal fraternity of the born child will attain jātāśauca, by which they are forbidden to perform any rituals for the next 11 (eleven) days. 
Nāmakaraṇaṃ, is the saṃskāra in which the parents or the father gives a name to the new born child. The name of the saṃskāra also means the same. This saṃskāra is insturcted to be done on the 10th or 11th or 21st or 100th day from the birth.
jananāddaṣarātre ṣatarātre saṃvatsare vā nāmakaraṇaṃ 
If the child's father is dead or not avaiable by any other reason , it is instructed that any one or any elder of the house should perform nāmakaraṇam.
yadvā piturabhāve ayogyatvamathāpi vāǀ anyo vā kulavṛddho vā jātakarmādi kārayetǁ 
After nāmakaraṇam, there is a small saṁskāra called as karṇavedha. Karṇavedha means piercing the ears. The ears are normally pierced by a sharp golden wire, which appears to be an ornament. It is advised to perform the saṁskāra before the new born gets his/her first teeth . It is advised to perform the saṁskāra on an auspicious day in the lunar month of kārtīka, puṣya, chaitra and phālguna, that too in the śukla pakṣa.
kārtike pouṣa māse vā chaitre vā phālgunepivāǀ karṇavedhaṁ praśaṁsanti śukle pakṣe śubhe dineǁ
śiśorajātadantasya māturutsaṁgasarpiṇaḥǀ sauciko vedhayet karṇau sūchyā dviguṇasūtrayāǁ
After nāmakaraṇam, there is one small saṁskāra called as 'niṣkramaṇam'. Niṣkramaṇam means coming out. In the present context bringing the new born child from the place of his/her birth is called as niṣkramaṇam. This saṃskāra is instructed to be performed on the twelft day, third or fourth month after the birth. On this day the child should be shown to the Sun and the Moon.
niṣkrmaṇam candra-sūryadevatādarśanaṁ ca dvādaśehani tṛtīye chaturthe vā māsi kuryāt. 
Annaprāśanaṁ is the saṁskāra in which the child is fed solid food for the first time. It is instructed to perform the saṁskāra on the sixth or eight month from the child's birth. Or which ever time felt to be auspicious by the elders of the family. The saṁskāra is to be performed after the child gets his/her tooth. A sweet dish made by milk, jaggery and rice, called as pāyasaṁ, is fed with a golden spoon or ring by the elders.
tatonnaprāśanaṁ māsi ṣaṣṭhe kāryam yathāvidhiǀ aṣṭame vāpi kartavyam yacceṣṭam mañgalam kuleǁ
ṣaṣṭhe māse annaprāśanam jāteṣu daṁteṣu vāǀ
After annaprāśanaṁ, on the same day a small display of different objects is arranged. The child is placed in front of the objects and the elders observe which object does the child touch. The objects that are place normally are - pen & book, gold, knife, cloth, utensils. It is believed that which ever the object the child touches, he makes a living related to that object. For example, if the child touches pen and book he is believed to become well read and makes a living out of teaching. This occasion is called as jīvikāparīkṣā.
tasyāgratotha vinyasya śilpabhāṇḍāni sarvaśḥǀ śastrāṇi chaiva vastrāṇi tataḥ paśyettu lakṣaṇamǁ prathamam yatsprśedbālastato bāḍham svayam tathāǀ jīvikā tasya bālasya tenaiva tu bhaviṣyatiǁ
Chūḍākarma popularly known as Chaulaṃ is a saṃskāra that is performed at the age of three. This saṃskāra is instructed to be performed by the trauvarṇikas, i.e. brāmaṇa, kṣatriya and vaiśya.
Chūḍākarma dvijātīnām sarveṣāmeva dharmataḥ| prathamebde tṛtīyevā kartavyam śrutichodanāt||
Chūḍā means lock of hair mostly on the center part of the head. Till this saṃskāra is performed the child's hair is not cut or shaved. For the first time the boy's head is shaved with a portion of hair left mostly in the center part of the head. This saṃskāra is performed without mantra and shaving of the hair for the girl child. As the female is not permitted to shave her head till ones husband's death, this saṃskāra is performed by just cutting small portion of hair in all four directions and in the center.
Akṣrābhyāsa is a small saṃskāra performed at the age of five to start education of the child. The apt time for akṣrābhyāsa is prescribed to be some auspicious day other than the tithis - Ṣaṣṭhī, Aṣṭamī, Pratipad, Amāvāsya and Pourṇamī in uttarāyaṇa.
prāpte tu paṃchame varṣe hyaprasupte janārdane| ṣaṣṭhīm pratipadam chaiva varjayitvā tathāṣṭamīṃ||
riktām paṃchadaśīm chaiva saurabhaumadine tathā| evam suniśichite kāle vidyarambham tu kārayet||
It is instructed to worship – 1. Hari, 2. Lakṣmī, 3. Sarasvatī, 4. The preceptors of the school of thought (Vidyapravartaka) in which the child is being introduced and 5. The school of thought (Vidya) (in which the child is being introduced). After the worship the Guru (Teacher) should start the desired Vidya. At this time the Guru should sit facing east and the Śiṣya (student) should sit facing west i.e. both the student and teacher should be facing one another.
Pūjayitvā harim lakṣmīm devīm chaiva sarasvatīm| svavidyāsūtrakāraṃścha svām vidyām ca viśeṣataḥ||
prāngmukho gururāsīno vāruṇbimukham śiśuṃ| adhyāpayettu prathamam dvijāśīrbhiḥ supūjitaṃ||
Upanayanam is an important saṃskāra for the males of brāhmaṇa, kṣtriya and vaiśya varṇas. It is instructed to perform the saṃskāra at the age of seven (garbhāṣṭama) for brāhmaṇas. At the age of ten (garbhaikādaśa) for kṣtriyas. And at the age of eleven (garbhadvādaśa) for vaiśyas. It is instructed to perform the saṃskāra at vasanta ṛtu (spring) for brāhmaṇas, grīṣma ṛtu (summer) for kṣtriyas and śarad ṛtu (autumn) for vaiśyas.
Garbhāṣṭamābde kurvīta brāmhaṇsyopanayanaṃ| garbhādekādaśe rajño garbhāttu dvādaśe viśaḥ||
Garbhāṣṭameṣu bramhaṇamupanayīta garbhaikādaśeṣu rājanyam garbhadvādaśeṣu vaiśym vasanto grīṣmaḥ ṣaradṛtavo varṇānupūvyeṇa|
- Strī yadā akṛtasīmantā prasūyēta kathaṃchana| gṛhītaputrā vidhivatpunassamskāramarhati||
- jātakarma tataḥ kuryāt putre jāte yathōditam|
- jāte putre pituḥ snānaṃ sachailaṃ tu vidhīyatte|
- kuryānnaimittikaṃ snānaṃ śītādbhiḥ kāryamēva ca|
- mantravat prāśanaṃ chāsya hiraṇya-madhu-sarpiṣāṃ|
- yāvanna cchidyate nālaṃ tāvanna prāpnōti sūtakaṃ| cchinnanālē tataḥ paśchāt sūtakaṃ tu vidhīyatē||
- bahvṛca pariśiṣṭa, smṛti muktāphalaṁ, p.81
- smṛti ratnaṁ, smṛti muktāphalaṁ, p.81
- sāyaṇīya, smrti muktāphalaṁ, p.82
- smṛtyarthasāraḥ, smṛti muktāphalaṁ, p.82
- yamasmrti, smrti muktāphalaṁ, p.82
- logākṣismrti, smrti muktāphalaṁ, p.82
- mārkaṇḍeya smrti, smrti muktāphalaṁ, p.83
- manusmṛti, smṛti muktāphalaṃ, p.83
- mārkaṇḍeya smṛti, smṛti muktāphala, p.84
- Mārkaṇḍeya smṛti, smṛti muktāphala, p.85
- Manusmṛti-2|36, smṛti muktāphalaṃ, p.86
- Āpastaṃba dharmsūtra-4|10|2-5, smṛti muktāphalaṃ, p.87