C.L.
I live 10 minutes away from the Mall of America and have been to that waterpark several times. My kids like it, but we've never stayed at the Radisson. Ironically, we have a coupon for a free night there, but haven't had a chance to use it. I think it would be good for ages 5 and 8, although there are some slides and things they probably won't be able to use. There is a large play area in the middle especially for younger kids. There is a zero depth entry wave pool and a lazy river. It has a north woods/Minnesota type theme. There is a grill and snack bar. If you stay at the Radisson I think it includes admission to the waterpark. It is rather difficult to get around the Twin Cities without a car, unfortunately. You would be very close to the light rail line which would allow you access to the airport and downtown Minneapolis, but anywhere else you wanted to go (other than the MOA and the waterpark) would probably require a car. What other kinds of parks are you interested in? What time of year would you be here? Feel free to send me a private message with any specific questions you might have.
Edited: I'm glad someone else told you about the rooms with bunk beds. I just remembered late last night that my youngest son HAS stayed at the Radisson as part of a birthday party. They had one of the rooms with bunk beds and he loved it! Since it is attached to the waterpark I think the hotel tries to cater to families. There is also an arcade (not my favorite place).