Tour operators Thomas Cook and Jetair told the dailies De Morgen and Het Laatste Nieuws that 6% of the hotels in their air travel hotel brochures ban under 18's or in some cases under 16's and 17's.
Jetair's Hans Vanhaelemeesch: "Bookings for adult hotels are up 49%. There are no legal issues. Every service provider is free to decide on the group it intends to target with its service."
"Holidaymakers seek holidays made to measure. Some people want lots of animation for the kids or a swimmer's paradise. Others appreciate peace and calm."
Thomas Cook's Baptiste van Outryve says that demand is greatest during the spring and autumn.
Both tour operators stress that the lion's share of hotels accommodate families with children.