As a mommy, I can't think of anything worse than getting stopped and interviewed by immigration with a baby. For peace of mind, I would recommend you get a dependant dtv for you and your baby. The cost of the visa is pretty good considering it lasts 5 years, allowing you the choice to live in Thailand or not. I know you've mentioned you haven't decided where to live, but this visa gives you that freedom to choose. Children are resilient and adaptable to their surroundings.
You may be able to get into Thailand next visit, you may not. But eventually the luck will run out and immigration will start asking questions