my new friends are childish

so I've just started uni and have made one friend that I am particularly close with. we are now part of a bigger group of around 10 people but my issue is that majority of them act like they're 12 rather than 18. they push each other in crowded corridors, steal each others pens in lectures and will fight over seats. I was just trying to ignore it until someone made an anonymous comment on a social media page talking about the people I hang out with and how childish they are. I don't know what to do cause I'm good friends with one person in particular as well as a few others, but I don't really want to be associated with the really childish behaviour. I don't know if I just need to loosen up a bit but when it's annoying other people, I think it must be more so to do with them. I'm not sure if I should just spend less time with them but everyone seems to have found their 'groups' on my course so I don't know who is have to talk to. sorry if this sounds really harsh but I don't know what other way to put it. thanks in advance for any advice