I sail with kids under 10 regularly and they pick up on your tension, if you’re apprehensive they won’t enjoy it. The best thing I do with anybody new is take them in the shallows and teach them how to capsize and right the cat which is great fun to new people and gets rid of a lot of the fear. Most kid’s natural tendency when they’re capsizing is to climb high but that gives them a fall where they can injure themselves. When we’re going over the kids need to slide to the low side and grab any rope near the water so that they stay with the cat and they’re not allowed to let go until I come along and assist them onto the hull, as they get more confidant they scamper back on the boat quicker than I can. If your worried about righting, a power pole worked for me on my old Stingray, while I was hanging on the pole my daughters aged 7 and 9 at the time would stand on the hull and lean back holding the dolphin striker then as the cat came up they would scamper on to the tramp, if one didn't make it the other would pull them up. IMO definitely no raft, it would only increase the complication and the danger of getting separated. I think you’ll find the 5.7 an excellent stable platform for family sailing, it will carry the weight easily and steer normally as long as you’re not out in a gale. Enjoy yourselves
heres a photo showing a pile of kids on a 5.7
regards