Awesome! 4 is real young, I can tell he enjoyed it a lot!
I grew up on a large hog farm (large at the time, one of the biggest in the state back then). We had a small case skid steer we used a lot for pushing hog shit out of the corridors in or outside of the buildings. I was running that alone by age 9 doing that kind of thing. We also had a bigger case skid steer, and a couple of larger Farmall type tractors of course too. By age 10 I was helping dig ponds (usually a half acre or a little bigger in size) on our land with the bigger skid steer. We did bring in a local excavator to do most of the big dirt moving, but we did the final moving and misc ourselves. I clearly remember how cool it felt to be running that skid steer digging out the bottom of a soon to be new pond. Just had to make sure I didn't get stuck in the muddy areas. Dad had 4 manure pits and 4 fish ponds on our land. We stocked the fish ponds ourselves, usually went over to the Verdigree area where there were lots of ponds farmers didn't mind we fished and took the fish back to our ponds. Dad had a cattle water tub in the back of the truck, that's how we transported the fish we caught. Was fun.
I still prefer Case skid steers to this day BTW. The models from the 90's are tough to kill. Which I had two of when I was building houses in Lincoln before I moved to MT. You can learn a lot of translatable skills growing up on a farm.