Hi there
We have been going since our son was 5 months old. We have been for the past 3 years and each time requested a cot and each were told they will request but cant guarantee. I was always panicked and worried until we arrived.
When you check at the cheyenne just ask at reception if there is cot, they tell you there should be one but if there isn't just call reception from your room request one and they will bring it along. We never had any problems and it arrived within about half an hour of us arriving.
With regards to your youngest not being on the form, don't worry our son is only on there this year because he is now 3 but has never been on there before, but our nephew isn't on there this year because he is only a year old. They don't put them on because they don't need a disney pass or a bed.
You and your family with love the Cheyenne, our son and niece love it. The cowboy theme is great.
Have a lovely time.
Lisa