There are two water parks on the island, both on the West coast.
Aquarock Park by Calan Bosch Marina is a great place for older children offering a go-kart track, trampolines and a large swimming pool with waterslides - www.aquarock-menorca.com/UK/indexUK.html
Alternatively, try Aqua Centre in Calan Forcat. There is a go-kart track as well as a swimming pool and waterslides, and a games arcade with a covered eating area - www.aquacenter-menorca.com/
Castillo Menorca, located on the main road between Ferreries and Cuitadella, has an adults pool with a water slide and a childrens pool, as well as mini golf, trampolines, a childrens play area, a shopping complex selling leather goods, jewellery, ceramics and gifts, a snack bar and a fantastic go-karting track! WiFi is also available - www.castillomenorca.com/servicios_en.php
In addition to the above, several resorts also have water slides or splash pools, the largest being in Son Bou. Smaller slides for younger children can be found in Calan Porter, Cala Galdana and Cala Blanca.