I had a reusable type shopping bag that I wore on my shoulder as we made our way through the baths to Devil's Bay - It never even came close to touching the water. The water was never higher than mid-shin. At the entrance to the trail there is a section off to the right that will take you through deep water, but it doesn't go thru. People who wanted to explore that area just left their bags and shoes where it was dry. The trail that goes through is off to the left and as I stated before the water was never higher than mid-shin. There is some ducking and crouching that you have to do at a few points, but as long as you don't have a back or neck injury or issues or knee issues you should be okay. While we were there I saw people young and old of all ages and ability levels making their way through. If you'd like to go check out Devil's Bay and avoid maneuvering through the Baths there is another trail from the top that leads down to Devils Bay. I'm not sure this distance - I think it's probably about twice as long the trail to the beach at the Baths (it took us about 20 minutes), but it's a pretty easy hike that my entire family did in our bare feet. If you have Tevas or Chacos already they would probably be a good choice, but I don't think it's necessary to purchase new shoes just for this excursion. Flip flops and bare feet were sufficient for my family. We did wear tennis shoes initially, but it was complete overkill in my opinion (and then we just had extra stuff to carry around). My kids are 9 and 12, but I would have been completely comfortable on the trails there and exploring the baths with them if they were 4 and 7.
My husband and I are middle aged and in relatively decent shape and free from injury and exploring all the trails didn't seem strenuous at all to us. I'm sure you could do a google search and find plenty of
youtube videos people have posted of the trails.
At about 1:49 in this video it shoes one of the most narrow places you'll have to crouch through at the start of the trail through the baths.
And while it's really shaky, this video shows the ladders you'll have to go up and down. My recommendation would be to turn around and climb down FACING the ladders when going down (the opposite of what these people did). That's what our tour guide recommended and it was really easy to maneuver.
Hope that's helpful.