Use sunset as your turnaround alarm.
This is the Zion hike you can do with a toddler and still feel like you saw something. The lower trail leaves from across the road at Zion Lodge and runs 0.6 miles, almost entirely on concrete, though a couple of pitches steepen enough that a stroller becomes a two-person job. The waterfalls are seasonal, so in a dry stretch expect a drip rather than a curtain. Going on to the middle and upper pools trades pavement for dirt and real climbing.
Waterfalls dripping over alcoves into green pools. Lower pool is stroller-ish.
Heat note: desert country - in summer start at dawn and carry more water than feels reasonable.
Water bottle, sunscreen, hat, snacks, comfortable shoes.
Make it a weekend: South Campground (Zion) (Camping, 4 mi) · Watchman Campground (Camping, 4 mi) · Lava Point Campground (Camping, 10 mi) · Kolob Reservoir (Fishing, 14 mi)
More hikes nearby: Angels Landing (Hike, 1 mi) · The Narrows (Bottom-Up) (Hike, 2 mi) · Riverside Walk (Hike, 2 mi) · Canyon Overlook Trail (Hike, 3 mi)