Personally, I wouldn’t do it. I don’t think they’re safe 🙁
Young kids’ legs and ankles are particularly susceptible to damage from twisting forces. I’ve seen a couple of youngsters in hospital with breakages resulting from ski bindings incorrectly adjusted.
I assume you’re thinking “just for a novelty, bit of fun to walk around in” rather than to actually ski down a slope on. Even so, they’re not going to release when the youngster falls over.
Problem will likely be that your youngster may want to do a bit more than just walk accross the fields. Five is definately plenty old enough to try skiing proper. My youngest was on skis at three. There’s plenty of suitable stuff about and they’re seldom expensive on ebay.