Only 2 hrs 30mins away from London on Eurostar. Take the kids to Mini Europe, a giant model village. Children under 4ft go free/adults 312.50/Kids over 4ft £6. Then visit the vintage cars at Autoworld at the Parc du Cinquantenaire. Older children will enjoy the Belgian Centre for Comic Strip Art, atribute to Tintin. There are plenty of edible exhibits at belgium's Museum of Cocoa and Chocolate.