First of all, I love your screen name!
Your little one may not be tall enough for Splash Mountain. Is he 40" tall yet?
Haunted Mansion does depend on the child. One of my daughters has loved it since she was very small. I have an almost 20 year old, who is still afraid of the things that pop out suddenly, so she still won't ride it. She was probably almost 4 when she rode it for the first time. LOL!