If parents holding valid RP, then they can bring baby within 90 days from the date of birth.
Carry the passport,birth certificate of baby along with you while travelling.
Show this at Kochin/TVM airport or wherever you are travelling from and tell them that for baby's aged less than 90 days can enter to qatar without visa if parents are having valid RP.

Also attest the birth certificate.

Sometime the immigration officer might be asking unwanted questions bla bla bla. But tell him very clearly about this.

Please cross check with your friends too. I had taken my child with me in 2009 and after that went to immigration straight away and stamped visa for two years.

Hope this helps.