children

Just goggled it. It has play areas for children from age 2 up age 12, so yes, it probably is a good one for a 5 year old.

It's worth a visit. Also, on the other side of Brussels, just driving round the ring to exit 19 (I think) is the park at Huizingen:
http://www.365.be/attractions/att/recreation-recreation-aquatic-centre-h...
It's brill.

Jette is full of great parks and green areas. I confess to not knowing that one, but nearby is the bois de Dieleghem which links on to the large and varied parc Roi Baudouin, which links on to the Poelbos nature reserve, which links on to the bois de Laerbeek. Paradise for outdoor-minded kids.