Do NOT expect anyone to stand up for you just because you have a child. I've been on SO many buses at WDW and have been horrified at what our society is like anymore. Young teens and young adults stay sitting while elderly people try to balance on a moving bus. Moms allow their one and two year olds to have their own bus seat when there are people standing. Disney gift bags are piled on an otherwise empty seat. UGH.
TRUE STORY. My ds was about 3 1/2 yrs old when we were leaving a park one evening. He fell asleep as I carried him to the bus. The bus was pretty full and it ended up being standing room only. NO ONE offered me a seat. I stood (unable to hold onto a pole b/c I had both hands holding my son up) attempted to balance on a moving, turning, braking bus. Several times I nearly fell into the person's lap who was sitting next to me and that person gave me a dirty look!! HELLO!!!! UGH! Now, it'd have been one thing if every seat on that bus was filled with someone handicapped or elderly, but it was filled with able bodied (albeit tired) people.
I was VERY impressed on this last trip to Disney when a bus driver was packing people into his bus (the line was still VERY VERY long) He made announcements like "if you are standing facing the side of the bus, you are taking up TOO much room, turn so you are facing the front of the bus and then move back." Another was "I am not moving this bus until we get more people on." And my personal favorite "There is a woman coming on the bus right now holding a small child. I expect someone to do the right thing and offer her your seat. If you do not offer her a seat, I will pick someone to GIVE her their seat!"