We've stayed at BWV before with our grandkids, and they've all gone down starting at age 3-4 with life jackets on. You can get them (free) at the community hall. I couldn't keep up (stairs) with my 4 year old DGS last year, he wanted to go again & again.
You can't go with them, each rider goes separately.
The water is 5 ft appx at the bottom, and with the water coming out of the slide, it's quite a torrent, so without a life vest they need to be a pretty good swimmer. MY 7 & 9 year old DGD's handle it now no problem, but I'm still at the bottom waiting for them to help get them over to the side.