Hi, Amy! Looks like your Magic Kingdom day is the day after Mother's Day. Feel free to give your husband a suggestion [
wink-wink, nudge-nudge] to drop us Disney Dads a line for ideas on how to make Mother's Day special for YOU (brunch suggestions, spa services, floral hook-up, etc.)
The crowds at Magic Kingdom on Mon., May 9 should be moderate. You won't be packed like sardines on Main Street. And hey, speaking of Main Street, the
Main Street Vehicles are rad. They're somewhat infrequent though and they'll only take you one way down Main Street. If time is the main consideration, it's quicker to walk.
The
Walt Disney World Railroad could save you a couple minutes if you don't spend much time waiting to board or disembark. (I laugh as I write this because I'm usually the pathetic guy having difficulty hoisting the double stroller on and off the train. I do get better with practice, though!)
It's best to look at the Main Street Vehicles and the Walt Disney World Railroad as attractions. If the railroad ends up saving you some time, consider it an added bonus.