When taking photos with our little one at the age of 2.. he wanted out to see them and interact... so while waiting in line we'd unstrap him and he'd jump out...the 4 older ones would keep him entertained til it was our turn. When he was tired he just staying in his seat and the characters had no problem interacting with him from there.
Same with Nan. We just have them hop out and get in line and try hard to keep them busy. Or depending on the line set up, wait next to them with stroller kid, and then have them hop out when its closer to our parties turn.