If it's raining you couild try leisure world near the galway shopping centre on headford rd. Indoor soft play area - bowling if you can stand the screaming kids. Never been myself - their website is pretty useless - no details about galway at all - but they are open I saw an ad today in a free weekly paper.
Also you might try turoe pet farm near loughrea - they have special activities for easter on Sat and Sun
I quote "
Cuddle and feed the animals, visit the pets corner, and follow the nature trail. Indoor play areas include Ireland's first "Inflatable City", a ball pond, adventureland, bouncing castles and games room. Outdoor amenities include a football pitch and playgrounds with swings, slide, and a tree house. Other Facilities: resteraunt, picnic areas and BBQ on request. For bookings contact Patrick or Mary Corcoran on 091 841580."
Again - not been myself but just saw the ads today in a free paper for Galway. Might give them both a try this weekend myself.