Thanks for the reassurance Flecc - I think I just need to make sure the kids know not to climb onto the bike. They haven't yet but I wouldn't put anything past them!The propstand is perfectly ok of there's no additional weight on the bike, failures usually result from excess loadings. For example, abruptly jolting the bike down onto the stand leg, being seated on the bike and letting it lean down onto the stand leg, propping onto the stand with a very large pannier or carrier load.
Although the Granstand one you link to holds the bike roughly upright, it can stress the rim and/or spokes and lead to an out of true wheel, so I don't favour that type at all.
.