I think the AZ Science Center recommendation is coming because you're already staying downtown and you could probably walk there. It is fine, but if you've been to other science centers, unless it is a rare rainy day, I'd probably take a miss.

Rawhide is ok, but it is out near the Gila River Casino now. You'd be backtracking to go there, then would have a long drive out to Goodyear. You could stay near Rawhide if you want to visit there (unless you're tied to staying in downtown Phoenix).

The Botanical Gardens and Zoo might be something worthwhile for the kids, and it isn't far from downtown. In theory, you could even take the light rail, then they have a bus that connects from the light rail to go to those locations. It is close to downtown Tempe, where you could do like Wilbur suggested, boat on Tempe Town Lake. You could grab something to eat on Mill Ave, hike up A Mountain, etc.