How Many Kids To Invite To A Birthday Party?

  My daughter Marissa (pictured) is turning 7 next month and we are putting her kids birthday party together.  So the question is, how many kids should she be aloud to invite?

I had her write down what kids from her class she wanted to invite.  She gave me 20.  i asked how many kids were in her class and she said 23.  Ugh. 

Not to mention family kids, family friends and her friends from dance class, we are looking at 40 kids for her birthday party.  It seems excessive to me, not to mention pricey. 

So I need your help.  How many kids should she be aloud to invite?  Please let me know below.

Thanks!