People of all ages can visit the steam vents at Hawai'i Volcanoes National Park. It's got the typical raised deck walkways with railings to protect you from falling into the steam vents. There is a lot to see along the way, too. From the tall grasses with shallow root systems to the wildflowers, to the illustrated billboards of people falling into the steam vents.
The day I was there was the first day of the Trump government shutdown. And the park was packed. Although partially closed, Volcano House was open and a few attractions. It was free, too, because there were no employees at the gate to collect entrance fees.
You can read more in my personal blog today and see a ton of photos at this link: Steam Vents at Hawai'i Volcanoes National Park.