I usually park at East River Flats, $10 to park but it's easy in and easy out usually. Good spot to tailgate and hang out for a couple of hours before the game. The only drawback is it's about a 1/2 mile walk from there to the stadium so consider that your kid would have to walk that which would be a challenge unless they are about age 10?
394 to East Bank exit, across the river and then take the first right, stay right until the next street, a left and then you will see guys with flags waving people in on the right hand side. We usually walk to the parking ramp, take the elevator up a couple of levels and you end up right behind Coffman Union.