@Musstapha ********
For a ME Non-O Visa based on marriage (and I believe it applies for supporting a child), your entry stamp is only valid for 90 days. You are free to leave Thailand as many times as you desire, as many times as desired through any border you desire (pending approval from the other country, of course).
You do have to leave Thailand within the 90 days.
1 day before the visa expires, you can cross out of Thailand for another 90 day stamp (that'll give you 15 months).
Before your stamp expires, you can extend it by another 2 months (60 days), giving you a total of 17 months on one visa.