If you go to the Grand Canyon with a 2 yo you will be a nervous wreck the whole time. Most of the paths run pretty close to the dropoffs. When we went with our kids I was so glad they were no longer toddlers.

Ruby, you asked about the weather in New Mexico. It's true that if you are looking for warm Florida-type weather, New Mexico won't work in March. The weather ranged everywhere from 30 degrees (snow one day) to 70 degrees while we were there. We had along a fleece jacket and windbreaker for everyone, so that layering was a possibility. Most of the time, we were in jeans and sweatshirts. Hats and gloves came in handy once or twice.