You will probably be best of going to the Antalya area as it is very early in the season. It doesn't really start until May and the weather could a bit unreliable, the climate is slightly better around that area at that time of year.
The bars and restaurants may not all be open and it is usually pretty quiet. However, its a lovely time of year for exploring, and the spring flowers will be lovely Also good time to hire a car and do some sightseeing, if your 4 year old is content with that.
If you are looking for a lazy time in the hot sun with entertainment for your child, it may not be the ideal place at that time of year. I think the all-inclusives are reasonably busy then, but sounds like that is not what you are after.
I hope you are able to find something that suits you.