Playdates with Twins

C, who is 4 1/2, would like to have a playdate with his friend H (in his Pre-K class) on Friday afternoon. H has a twin sister, also in C’s class, and I am wondering if I should also invite her over to play. I think that C would prefer to just have H over without his sister, but I’m sure that they would be fine if she came along. 

So, my question is two-fold: 1) Parents of twins, particularly twins who are boy-girl, do you usually prefer to have both of your children invited on a playdate, particularly when they are so young? And 2) How have other parents dealt with this issue when inviting children over to their house to play?

Thanks for any advice you can give me!