I climbed Dunns River Falls about 16 years ago with a small private group from a resort.
At the time, it was required to hire a Falls guide to climb the falls. Back then, the guides did not have a set rate.
Many of the rocks you climb over are large, and at times very slippery. A few of the people in my group had difficulty. I noticed other groups taking different paths so perhaps there is an "easy route".
When you get to the top of the climb, there is a vendor area. Some of the
vendors were pushy with the slower-moving tourists. None of the vendors bothered me, but then again, I walked through too fast for them to catch me
I don't think it would be a good idea to take a 4 year old on the falls climb.
I believe nowadays there is a viewing deck and a seperate walkng path which leads to the top of the falls. It would be possible for the 7 year old to take an
easy falls route while the 4 year old took the walking path with a parent.
Hope this info aides you in the decision process.
Dawn