We ate at De Spelleplekke with three other families. All together we were six adults and seven children. Not an easy group to seat.
The staff were very helpful, we had a nice roomy spot next the play corner so the children were occupied during the lull between ordering and eating.
DO try their Thai beef salad. It's delicious. They also have a large choice of children's meals. I had lovely Thai-style mussels.
If you're going to the Belgian seaside and end up in Oostduinkerke, don't bother with the other restaurants. Just go here.