In Phuket Immigration office.

Copys.

1.Baby's birth certificate.

2.Baby's house book.

3.Mother's thai i/d.

4.Mother house book.

5.Copy of your Passport pages.

6.Notification form for house-master, owner or the possessor of the residence where you has stayed.

You get that form from internet or Immigration office.

7. 1 Passport picture.

In the Immigrant office they will give you also 2 different form where you put your details and reason for extension.

This is for 60 day visit thai family extension.

Best is that you go Immigrant Office and ask what they need.

Sometimes rules between offices can change in the land of the smile 😉