[ARCHIVED] Can't travel with more than 1 or 2 Sims

I commented on this post before as it happened ages ago. Can't remember what I did to fix it or if it sorted itself out. It has just happened again though. My child sim brought a friend home from school. After finishing homework I wanted her to go to the park with the boy and their two other friends. The only thing I can think of is did this happen because the boy was already at her house but the other friends weren't? In the end I sent my sim and the boy, then invited the other girls when they got to the park.