hi

If i go into a restaurant and ask for a table for 7 people , do i say...bir masa yedi kisilik veya bir masa yedi insan

Also  if i want a high chair for a small child can i say...yuksek bir sandalye var mi?

You can say; Yedi kişilik bir masa lütfen.

You can say that and they will surely understand what are you asking for. But you better call it "çocuk iskemlesi" (or "çocuk sandalyesi") and they will bring it to you if they have any. 

cok sagol

thanks for your help