Is it possible to buy house in my Thai son's name and then lease?

No. We understand that you are talking about the land attached to the townhouse and that answer is for that:

1. There is no law to limit the age of the owner of the land. So technically, your son could be the owner of the land. However, the land departments have a lot of discretion to accept or not transactions. Because your son is a baby, they might want the mother to be the owner first, and then, the mother can give the land to the child.

2. However, once a child is the owner of the land, a child can NOT lease it to anyone EXCEPT with the authorization of the Court. You will find these limitations about real estate and children at clause 1574 of the Thai Commercial and Civil Code. Yours is 1574 (1).

A lease between husband and wife might also be refused by the land department. Few years ago, it was easier, right now, the land department will normally agree on the registration of a usufruct but will refuse a lease between legal spouses.