my friend entered from Australia on passport. I have heard one can have an extension of 90 days for visiting Thai wife and child that have his name in their ampur book. An Immigration officer told me this.

One can obtain a 60 day extension for visiting Thai wife/child.

Police Order 777/2551

2.24 In the case of an alien visiting a Thai spouse or child:

Permission will be granted for a period of not more than 60 days at a time

(1) Proof of relationship.

(2) In the case of a spouse, their marital relationship shall be de jure (legitimate) and de facto.