It is a good idea to assign one adult purely to supervise small children.
Buoyancy Aids - Small children should always wear buoyancy aids when in the boat cockpit/rear deck, on locksides or walking/playing near the water’s edge.
No running - Persuade children especially, but others as well, not to run along the side of locks.
On the roof - Children (or adults) should not be on the roof whilst the boat is in a lock or on a river.
Don’t be upset if someone points out these dangers. Most owners are aware of the need to keep dogs under control. On the waterways, especially at locks etc, uncontrolled dogs can be a hazard.