The key in teaching your children to do anything is patience. It's harder with your own kids because you want them to do it perfectly. Get past that, realize that some bangs and maybe a few dings are part of the learning process and learn to sound calm. Practice saying things in a calm voice like "It might be a good time to reduce speed." "What is your depth now?" And "It would be a good idea to give that towboat a wide berth."
I was docking a boat before I ever drove a car. My uncle took me out in my dad's 28' Owens (Single 327) for a while and I learned to dock by doing it repeatedly--kind of like the touch and go method they use to teach pilots how to take off and land--until I could do it well. This proved a slight handicap when learning to drive a car because I kept trying to account for the wind and current.
Had a few hard landings over the years, but (thankfully) never any major damage. (Most of my mistakes buffed out.--Big Ms are good that way.) My uncle, a safety-consious professional captain, taught me the biggest trick: take it easy, take your time. A slow approach will almost never result in disaster.
Good luck and safe boating.
Joe
Joe
1977 28' Express
Twin 318s, raw water cooled
Ohio River