Try not to worrt about it too much. Little ones cry. It's just a part of life and MOST people at Disney are going to underdtand and sympathize if they hear a little one crying on a ride. Do whatever stuff you normally do (that's safe and possible ofcourse) to try to calm them down, maybe throw out a quick "I'm sorry" to those around you and understand that a lot of us have been there. Whether it's on a ride, in a show, at a restaurant, on the bus, the plane, whatever--- just about every parent has had their baby/toddler cry in a place that may disrupt others.
Some tips that may help:
- For the tame boat rides and such, we carried a small bag with us that had a snack, a sippy cup, and a small toy. The snack we would reserve for lines or if we really needed to in a show, but the sippy cup and toy came out a time or two on the rides when needed.
- Point out the different scenery, the colors, whisper to them about what's going on, cuddle them. If it's the scenery or ride itself that's upsetting them, let them bury their face in your arm or chest and rub their back. They typically aren't going to care on the boat rides if you pull your little one onto your lap during the ride.
- Always double check diapers before getting into any line to avoid any crankiness from that.
- My toddler tended to snack and drink a lot at Disney. Small things to eat settled better in the heat than a normal sized meal, but it meant he was hungry more frequently, and of course would be grumpy when he was hungry. So make sure to bring or get snacks frequently and drink LOTS of fluids. Have a quick snack before getting on a ride if they seem hungry/thirsty.
- Know how your kid is when they are tired/ how they nap. My son was happily lulled to sleep on iasw and the Carousel (thankfully I had an arm around him!) but for other kids, the rides can be too much stimulation when they're sleepy. If they are sleeping, don't wake them up to take them on a ride.
I hope this helps and that you have a fantastic trip!