As a former 4-year old sailor, I have fond memories of:
1) Playing in the V-Berth.. It's like a kid-sized bedroom! Falling asleep there is good, as well..
2) We used the sail bags and pretended they were pizzas. We had a pizzeria in the cabin
3) A small fishing net on a pole to scoop up interesting things that float by.
4) When I was about 5 or 6, I made my own sails. that is, I put a couple of sticks together and made a mast and boom. I made sails out of muslin and put an insignia on it (Shark #106) ... I put my sailing rig in the cam cleat on the aft cabin top, and trimmed my sails accordingly. My dad said it made the boat go faster. I'm sure it did. She may be a bit young to make her own miniature sailing rig, but I bet you could.
No surprise that over 40 years later I still have sailboats!
1987 CS 36 Merlin "Kyrie"
"They drove a dump truck full of money up to my house. I'm not made of stone!" -Krusty the Clown