Janbo25, Hyde Leisure Pool is great, wave machine, sprays, whirl pool, rapids, slides, jacuzzi, steam room, sauna, etc...
even though we live 20 miles away it well worth it
J3 of M67, then right, past Morrisons, left, then follow signs
Manchester art gallery has a kids interactive area too, for say an odd hour
Manchester Mueseum of Science & Technology is great for kids, it too has a creche/kids play area on the top floor of the main build. Kids love the steam engines, planes, rockets, computers, etc...! (Castlefields area)
Just a few thoughts..