Prairie Heritage Park in Altoona has a small splash pad in the Civic Plaza area next to Hy-Vee. I wouldn't make a special trip for it, but it's fun to combine with the Enabling Garden nearby, which is a 0.17 mile walk via paved trail. Or if you want to go a bit further, it's a 0.43 mile walk to the Altoona Library playground and storywalk.
SHADE: shaded area with benches + shady grassy area
RESTROOMS: inside Hy-VeePARKING: off-street parking