I think it really depends on the child.
For children in my toddler group (years ago), big come-to-life characters were dicey...some of the children loved it, and some were very frightened and burst into tears, needing adult arms for security. (This was the local cute supermarket bear mascot, as benign as can be, who came to visit.)
Also, if your child is able to hang out and watch something for a while, that's one thing, but if they love to run around, a larger venue could prove to be hair-raising. Many colossiums have tiered seating, so there's also a risk of falls for little ones who busy. And with that many people, there's potential for a running little one to get lost.
Just some food for thought...