@nishad,if you and your spouse have rp then you can bring your baby directly to qatar.
At the airport visa on arrival be issue to your baby.
later go immigration,submit your rp and your wife rp along with passport copies,baby medical copy then your baby rp will be issued immediately.

@Manij,for baby visa no need to submit all the required documents which you had submitted for your wife application.
for more info check the MOI website.