In my case when i broght my baby, they checked only the passport. They requested for some additional documentation for proof and then i had shown the birth certificate. But most of the script in birth certificate was in the regional language and they seem to have understood nothing. still i was allowed to get in with baby. Also they were not looking into the embassy attestation.

So, i think the attested birth certificate is not mandatory to bring in the child.

Anyways i would suggest you to have it attested becasue it may be required when you apply for the RP for your baby. Also, these kind of things are not too hard and fast here. So, better avoid an embarassment.