It's either exit 6 or 7 off the E411, motorway to Namur/Luxembourg from Brussels direction and well signposted. About 20 minutes from Brussels. Very popular, long queues on certain days, as it's June you're going there shouldn't be too many kids as schools dont finish until 1st July, has lots of amusment rides, food terrible. I liked it, plenty of the rides are pretty scary by my standards but I've only ever been to Portaventura near Barcelona so I'm not an amusment park expert. Had teenage visitors (13 and 15)who went there and they loved it. Their stepdad collapsed on the couch after a day there if that's any indication of how it is.
There's an aquaparc onsite as well, think it's called aqualibi.