Ledges State Park is our favorite place for creek splashing. We park in the Flood Pole parking lot, which has plenty of parking available and easy access to the creek. Then we walk the creek for half a mile up to the stone bridge and head back, for a total creek walk of 1 mile.
Iowa Parklands has great maps available. It's definitely worth the 99 cent charge to download the Ledges map. Here's a portion of it which shows where we park and how the creek meanders on both sides of Canyon Road.
The only downside to visiting Ledges is that it's a very popular park and can be very crowded. For that reason, I'm happy we're able to visit on weekdays. We arrived early and only ran into a few other people.
Due to the current drought in Iowa, there's less water in the creek than usual but still plenty of water to splash in. My kids love all the opportunities to climb and jump while creek walking.