Most clubs and associations are winding down for the summer just now. It may be difficult to find much going on in town when you get there. (This is normal for France in the summer.)

Things will pick up considerably in September with the big Rentrée. But for little ones like yours, there isn't much of a choice of schools if you're planning on putting them in the public schools. La maternelle starts most places as soon as they are potty trained. You may want to inquire at the mairie about a crêche or halte garderie for the younger child. The mairie should be able to give you information about the local schools - and possibly even sign your son up for the fall.
Cheers,
Bev