The Law Code of Yājñavalkya 3.1.5

3.1.5

ūne aparipūrṇe dve varṣe yasyāsāv ūnadvivarṣas taṃ pretaṃ nikhanet bhūmāv avaṭaṃ kṛtvā nidadhyān na punar dahed ity arthaḥ | na ca sakṛt prasiṃcanty udakam (YDh 3.5) ityādibhiḥ pretoddeśena vihitam udakadānādyaurdhvadehikaṃ kuryāt | ayaṃ ca gandhamālyānupalepanādibhir alaṃkṛtya śucau bhūmau śmaśānād anyatrāsthinicayarahitāyāṃ bahirgrāmān nikhananīyaḥ | yathāha manuḥ |

One who has not completed two years of age is 'under two years of age'; one should bury that deceased child, meaning one should place him after digging a pit in the earth, and not cremate him. Nor should he perform post-mortem rites such as the offering of water enjoined for the deceased by verses such as "They pour water once" (YDh 3.5). And he should be buried outside the village, after adorning him with perfumes, garlands, unctions, and the like, in pure ground other than a cremation ground, devoid of bone collections. As Manu says: