Not sure if it's nice enough for you, but I think that the Delta Montreal has a children's centre... I've never stayed at the hotel personally, but it's very close to 2 different Metro stops.

Unfortunately, most of the best hotels in Montreal are all smaller boutique hotels, but they don't offer much (if anything) in the way of amenities for children. Many of them don't have pools either.

So it might be a little tough to find somewhere that will keep everyone happy.

Maybe someone else has other suggestions?

baby_beluga