A lot of events have a 10 child minimum which is why two daycare providers used to share the cost and do it jointly in whoever's house was bigger.

What you might do is look into something less elaborate since the kids are little and their experiences minimal. Having a teen come over with their pet guinea pig in a cage would be novel to the kids.

Have someone come and read a story to the kids - might even be able to count it towards community service if they don't get paid - win/win for both of you. Just having someone different doing will seem like it is a lot more fun for the kids then because you have the extra set of hands you can plan some more elaborate activities/craft/snack related to the book read.

For me I feel once they are in school there are so many outings and events they have to do that I don't feel bad that I don't do them with my little ones. Yes they enjoy it but they also enjoy just being.