Hi there
My parents have a villa in the South of France in the Languedoc region (see here) and we have spent lots of time there in March/April time.
It certainly is significantly better weather in the South of France than back here in the UK but that said, warm sunshine is not guaranteed.
We have been and it has been warm enough to have a dip in the sea and sunbathe on the beach. That said, we have had some very wet days too!
The weather starts to improve significantly from early April, so as every week passes, the weather reliability improves.
If you do decide to go there in April, make sure you find somewhere that has lots on offer - if you head for a resort that revolves around beach activities, then it could be a disaster. Instead, find somewhere that offers a range of activities so that if you are unlucky, there are plenty of things for you to do.
Are you tied to school holidays and therefore considering the Easter holidays? We were there over Christmas and on some days, we were in shorts and t-shirts on the beach!
If there is anything at all you want to know about the Languedoc, just ask!