You need to bring your newly born within 3 mths of this birth, get the birth certifiate attested from your country  & ask your wife  to carry this birth certificate and you id copy when coming back to doha..

at doha immigration they will see the birth certificate & your id copy... they will stamp the child pp after tat within 7 days u can apply for you childs rp

for obtaininf rp u need to follow the same procedure u did for ur wife

and also u need to go to medical for ur child