In case of a new born, he/she can get a visa on arrival till the age of three months. His/Her passport, birth certificate would have to be presented at the immigration. Follow the link:

http://www.moi.gov.qa/site/english/departments/PassportDept/sections/sec...

Otherwise, bring him/her on a visit or tourist visa. Follow the link for the forms.

http://www.moi.gov.qa/site/english/departments/Airport/sections/sec770/7...