It's used a lot abroad in the party destinations as well. I read that it is only dangerous if is inhaled in confined spaces or inhaled on it's own ( not combined with oxygen). When taken balloons are used, to make sure it is inhaled mixed with oxygen. It works because they can't cover their mouth and nose with the nossle of the balloon. I think apart from that it is one of the safer drugs. It is not illegal to buy as it is used in cans but is illegal to take as a drug. Make sure your child knows that they must make sure the room is ventilated and they use a balloon only to take it - if they won't stop taking it.
As above - the Government risk assessment argued against it because people might fall over and hurt themselves. So suggesting people sit down to do it would be sensible, along with making it very clear that no-one should ever put a mask over mouth and nose to do it, only use balloons.
Personally I think people ought to try it before getting pregnant, so they know before labour whether it works for them or if they get scared or sick with it.