I just wish there was a consensus. It is incredibly difficult trying to explain to a barely 2 year-old that just because someone else has been allowed to do something, that doesn't make it right for him to do it too.
We go to a Sunday morning soft-play/gym that is generally full of parents who are pretty good about enforcing queuing, not snatching etc, but there are always a small minority who make no attempt to do so. DS is in a copying phase where he will immediately attempt to do anything he sees another child do - which was particularly fun on the way out of nursery the other day when a much older child was doing her best to kung-fu kick the disabled access button and I had to drag away a screaming toddler who wanted to help her destroy it!
So DS will quite happily queue and go round the apparatus in the proper way. And then a couple of children started climbing up the side and pushing to the front of the queue for the slide. DS of course then wanted to do it and we finished up with a huge tantrum with screams of "boy did it" when I wouldn't let him do the same. He was then a little confused when, having queued for a go on the trampoline, another couple let their 2 older children get on it the second he climbed on so he couldn't play on it at all.
I know life isn't fair, but it is very hard to teach a small child to abide by social "rules" when other people seem to be playing by a completely different set of rules.
I don't tend to have the "sharing" problem too much as DS never sits still long enough for another child to get a toy off him! He also tends not to actually wrestle toys off other children, but he does watch them like a hawk, wait till they fall over/drop it and then swoop in, grab it and make off at speed, pursued by me screaming "DS, give it back!"