We rode in the front of the express monorail from TTC to MK twice last year, with DS, 4, and DD, 1. We were allowed to have our folded up stroller, probably because I was carrying DD in a sling.
I agree with the PP who mentioned sullen drivers. That was our experience, also, both times. We were never even offered the "co-pilot's" certificate for DS, who is a HUGE monorail fan. Regardless, it was still a great experience.