Go with your idea of rope along both sides,and John is right on the money with two ropes.It will make a difference with little kids.
I made my dock u-shaped and roofed it. You're close to the ohio river and may be able to find used barge rope in large diameters that will safely hold someone who leans/falls into it. I had found some almost an 1-1/2" that worked well for many yrs.
Any of the marinas or B&B Riverboats should be able to help you or steer you in the right direction.
Good luck
