I don't know about soleil- maybe someone else can hep with that (and try UK campsite too).
Thinking about the ages of your children with Valades:
There is a little club for 2 hours most mornings- very low key- craft with some games/songs. The person who runs it is usually a Dutch student but will speak enough French and English, and the children who go are predominately Dutch and English. There's also some evening activities- a small disco, a walk with lanterns etc.
The toddler pool is quite shallow- much more of a splash pool but big and usually quite empty. From memory, the main pool doesn't have a large area where your children could touch the bottom and is usually quite busy, however, there is now another pool so I don't know if that has eased things, or how deep that is.
There is a large part of the lake where your children could stand and play/swim and the beach area. To get to the inflatables you need to swim, or canoe/boat out. There is a trampoline one which my younger children loved bouncing on (and you can get on/off without having to swim) but the other one is really for older/more confident swimmers as you can get 'jumped' off.
There's no buoyancy aids available, so if you want to use you will need to take with you.
It is fairly easy to keep an eye on children here- it's all within a small area.
Lots of playground areas, which are spread throughout the site. The site is expansive, and the accommodation is located nearer the pool/lake than reception. You could take scooters BUT it is also hilly, so really only good for 1 way! (And I'm aware you're flying).
HTH