Sigma 18-35 1.8 is great for low light and around $799. It is the only zoom lens in the world with f1.8 normally restricted to primes. It's like having three 1.8 primes in one lens 18/24/35
The canon 35 f2iS is a very good lens and one of the only lens on a canon system better than f2.8 with image stabilization. It's around $599 and 35mm is great for your camera.
The 50 1.8 stm is a great lens at a good price but 50 is too tight for indoors and disney rides on your camera. Canon apsc cameras such as rebels, 70d, 7d have a 1.6 crop factor so 50 is 50×1.6= 80mm on your camera (and my 70d)
Some other good suggestions for cheaper are the pancake lenses. They are very small and barely weight anything. Perfect for walking around disney. The 24mm and 40mm stm are both f2.8 but don't have image stabilization. They are around $125 a piece
All around
In short I would recommend:
Canon 35 f2 iS for best all around prime (599)
Or
Cheap
Canon 24 mm f2.8 pancake for best cheaper option (125) f2.8 won't let in as much light as the others for darker rides
Or
Zoom
Sigma 18-35 f1.8 for best zoom (799) and make sure to choose canon mount