So they're not queue jumping then just joining their mates, if one of your friends was ahead in the queue would you ignore them and wait up at back and ignore them?
I've been on soft play dates where others have been invited along and I've been the one to invite the others, it's never occurred to me to be upset when someone did it to me?
How did they push you out? Did you make an earnest effort to participate or sit on the sidelines in a grump?
Sometimes these things are all about people's perception, I was once accused of being in a clique at my eldest daughter's primary because I was secretary of the ptfa and in the mornings I'd often chat to the mum's who were the chair and treasurer, none of us were proper friends (ie we were friendly but didn't socialise), it was mundane crud like have you ordered the rolls for the bbq, can you co-sign this cheque, here's the newsletter to be photocopied etc and a group of other mum's got a bitchfest on the dreaded Facebook and started saying we were all in a clique and excluding others from the ptfa, funny since exactly zero of these women had ever attended a single open and well advertised meeting. We were simply 3 women with children and jobs who used those 5 mins between arriving at the school and having to leave for out jobs to sort out a few mundanities. This other group took an amazingly different and incorrect view of it.
My eldest is now at high school but I'm back on school runs with the twins' primary school, I honestly don't care if any of these women want to be my friends or not, I don't have time for bitchy little groups who backstab whoever happens not to be there, I will happily chat to whoever is standing about.
Ironically I'm now have a role on this ptfa too (different school as we moved areas) and a lot of time I find myself chatting to to the other ptfa mum's, not because we're a clique but because we're passing those few minutes with mundane stuff again.
Another poster made a comment about someone being a pushy gran because they came to all the school stuff, I do that - I make a concerted effort to attend as much as possible because they are my children, I want to support the school and see my kids work, they are the most important people in the world to me and they spend over 30 hours a week in school so I like being involved!
I'm miffed now because I never get to queue jump at assemblies, in fact I'm always last in and get stuck standing because a member of staff has nabbed me on my way in about something ptfa related.
Sorry didn't mean to blather on so much!
OP it seems like the women you're hanging around with at the school gate aren't interested in as formal and constricted a friendship as you, maybe take up a hobby and meet like minded people or volunteer in the school and meet people that way.
Did I read right that you have one in school and one in nursery? Maybe during the hours you have no children look for a class of some description to join like slimming world (not saying you're fat just that seems to be popular), zumba, art stuff etc.
If you're unsure of where to find these things ask on your local areas selling paged on Facebook, they can be great for information, pick something you're interested in and and a friendship group will naturally flow.
Try to relax about it all, you may have overthought a lot of this.