Last time I was there, I saw a toddler at the falls. It's an easy hike to the falls, probably 1/2 mile or so. The Patapsco River is also nearby a playground, and that's an even easier walk. Make sure you get there early, as it gets crowded quickly.
It's a pretty short walk to carry the baby. Definitely no strollers. Early walkers won't be able to do much on this one, but they might enjoy playing with the water when you get there. Mine were probably three before they walked on their own for this one.
Great question. We have a seven month old and were considering the same. I think it's too rooty and rocky for a carriage. However, a baby that's secure in a carrier attached to your body ought to be fine. Just take your time and go slow. Also, note that (if you're planning on going all the way to the waterfall) there are a couple times you'll need to cross a small stream by stepping on rocks. It's very easy to do, but you'll have to be extra careful with the baby.
In a stroller probably a little difficult, but carried definitely :)
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