We have only had an extra guests one time. It was a younger 1/2 sibling. It was ok that they brought her, we had extra of everything. However, she was a troubled child and stole a toy while she was there.
I did bring dd8 to a party that her little brother (5) was invited to. It was at a swimming place. I took ds to the party and MIL dropped dd off after sunday school. I kept dd with me while ds did party activities (cake, games, pizza). We watched through a window. Then when it was time to go swimming she swam with the other kids. I did ask the mother and the people at the venue if it was ok. Both said it was fine, and they didnt charge per child. I still felt very akward having to do it, but MIL couldnt keep dd, she had some where else to be. So, it was either have her join us or ds would not have been able to attend.
I did bring dd8 to a party that her little brother (5) was invited to. It was at a swimming place. I took ds to the party and MIL dropped dd off after sunday school. I kept dd with me while ds did party activities (cake, games, pizza). We watched through a window. Then when it was time to go swimming she swam with the other kids. I did ask the mother and the people at the venue if it was ok. Both said it was fine, and they didnt charge per child. I still felt very akward having to do it, but MIL couldnt keep dd, she had some where else to be. So, it was either have her join us or ds would not have been able to attend.