If baby is born in India, you only have to get birth certificate attested from Home Ministry-India, Ministry of Ext. Affairs-India, Qatar Embassy-India & Notary-India. These all attestations you can do by giving to some reliable attestation agency.
But up to 3 months old baby, no prior visa is required. You will get On-Arrival visa at HIA - Qatar. Just you have to carry original & attested birth certificate with passport while traveling from India to Qatar. All the best !