We visited the sculpture garden on one of the hottest days in July, but my toddler had a great time walking the grounds and pointing out the spoon and cherry. The other sculptures are fun to look at too (although no climbing on them!). And there is a flower garden at one end that was just beautiful, with all the flowers labeled. We did two laps around the garden.
Because it's free ($3.50 for 24 hour parking or one hour free if you score a street spot), it's a good afternoon outing. Because it was so hot we went inside the Walker Art Center, which is less kid friendly but was still OK (see separate review).
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.