An exeption were these orange things you strap onto a child's arms, and inflate, which they can't really remove by themselves.
Those are widely considered NOT safe, a non-swimmer child is probably much safer without them than with them, as using them lulls the caregiver into a false sense of security and they pay much less attention to them. They also teach children the wrong posture for swimming/floating, which can be difficult to unlearn. In the US the common wisdom says that if you use them you must be in arms reach of the child at all times - but that's what you'd do without them anyway, so what's the point?
The idea that you'd leave a non-swimmer child unattended with them is, frankly, horrifying.
Try to imagine if you were less buoyant like if you had ankle weights on and someone tied two empty milk jugs to your hands. Your hands are suddenly not useful at all for swimming and you can't pull them underwater so now you're forced to hold yourself up by pushing your arms out.
Here's how it can look, and this makes it a bit clearer why it can be a hazard. https://i0.wp.com/renomomsblog.com/wp-content/uploads/2015/0... If it slips down to the wrists like this it's arguably worse than having nothing at all.
Is it possible you are thinking of something like Puddle Jumpers (look up an image online), which look like water wings but strap behind the child's back, and don't actually inflate? Those are, indeed, considered safe.
In general, I want people to have full market freedoms, but I put those water wings pretty near lawn darts in terms of danger.