The largest children's museum in the world by area, with five floors of exhibits, an IMAX theatre, a working carousel from 1917, the Lilly Theater, a dinosaur hall with real fossils, and the outdoor Sports Legends Experience. Plan a full day. With younger children, two days is not excessive.
The themed Power of Children exhibit (with the stories of Anne Frank, Ruby Bridges, Ryan White, and others) is unusually serious for a children's museum and consistently moves adults. Buy tickets online for a small discount. Parking on site is paid; metered street parking around Illinois Street fills up by mid-morning.