What to do present-wise if your DC has been invited to a "joint party"

[TooMuchCaffeine]

DS (5) has been invited to another joint party. Both the "jointees" obviously know each other well, but on both occasions DS only knows/plays with one of the party children.
Sooooo do I only buy a pressie for the one DS knows or do I buy one for both? I work on the assumption that the list of invitees was compiled separately and each child only invited children they know/play with.

I would just buy for the child you know.

If dc knew both we would buy for both, even if they only liked one. If we only knew one then we would only buy for one.

I would only buy a present for the child your ds knows. if he knew both then he would buy for both. pretty sure thats what happened at joint parties i've been to.

Depends really

DS1 went to a 3 way joint party, we only knew 2 of them and were only invited by that one. We bought a present for the child who invited him and a smaller token gift (in my case just a very small toy) for the others

I was thinking along the lines of only buying for the child DS knew which seems to be the consensus here - just thought I'd check first so as not to offend anyone

We've held and been to joint parties and the consensus definitely seems to be to buy for the child or children you know -- so if you know both, two presents but if you know only one then buy only for that one.