Child friendly hotel / BB / Apartment near the Belgian coast

We would like to take my parents to the Belgian coast for a couple of days around Ascension. We'd travel as 4 adults + 2 babies (2.5 and 10 months).

Does anybody have a recommendation for a place to stay? I was thinking of renting an appartment, but it seems that on school holidays they only rent it for a week.

It doesn't have to be right on the coast, a farmhouse or family-friendly BB would be perfect!

Thanks