In the future, if she really wants this to end, she can throw away the pennies jar and stickers - just put her foot down immediately with the behavior.
When he's completely out of line, he gets ONE warning to bring it back under control. After that, that's IT, he's done. He's done sledding, go sit in the car until we're all through. His mother would have to miss out too, but it's worth it.
This applies to other things as well - a child's birthday party, day at the park, playgroup, whatever. ONE warning, and then he gets roughly grabbed up and he's gone home where it's not fun that afternoon if the behavior continues.
His mother will have to miss out on some stuff but this behavior will end quickly.
She needs to discuss this with him before hand, when they're both calm and receptive, and let him know that she is there to help him learn how to control himself.
children do sometimes have this issue with sharing something, maybe timing how long they got to use the sled would be good say 5 mins each let him see the watch , its his sled so let him have the first go on it , make sure the others stick to the time frame allotted .Hold his hand when the others are using it, so he cant get in their way .Maybe suggest that the others get one of their own ...good luck
I wouldn't be at all concerned about his behavior. It sounds to me like he was tired, especially if he went sledding the day before. His actions say "grumpy" to me, and in deep snow it's a lot of work to walk up a hill with those little legs! I just don't think he really was up for sledding, and they get grumpy when tired. He's still very young, I wouldn't worry too much about this. It sounds like his mother is doing a good job with him.
He knew he had to share his sled and was willing to initially. There were 2 kids and 3 adults so sharing had to take place! There wasn't a big thing between him and his mom about this. He was even going so far as to stand in the way of his stepbrother so the brother would run into him--not hurting but then we had tears. He had been told to move out of the way and his "brother" had tried to move a couple of times to avoid hitting him! He was given wait time because it took him a long time to get up the hills--not a long hill but the snow was deep for his little legs. We did ignore him quite a bit and then he'd "fuss his way up the hill" and go down the hill and it would start all over again! If you ask him when he's calmed down why he acted like that he can't normally tell you! He's being 4 with a vengeance!!
Sounds like he does this to get attention, children of this age dont always like to share, was there an issue with his mom about him sharing his sledge ?