pitching mound

It’s not difficult. Tell him to build his own. He will take better care of it that way.

https://www.instructables.com/DIY-Pitching-Mound/

We built one a few years ago pretty much like this one.

I built one similar to Good Knight's link as well but with some modifications.  I made it slightly wider and I extended the rear of the mound with additional flat space for some extra comfort room when the pitcher was working from the windup.  It also reduced "fall offs" when the pitcher was receiving a throw back from the catcher.   I added rubber yoga mat material, gluing it to the plywood before putting the turf over top (a large strip from about a foot or so behind the pitching rubber almost all the way to the bottom where the front foot lands, not quite full width of the mound).  It provided a bit of cushion and reduced wear and creasing of the turf and allowed a bit of give for the occasional kid that would get on the mound with cleats.  Lastly, I screwed two grip handles at each end to make it a little easier to lift and carry.  That said, my mods made it heavy.  I was able to move it around the yard but I wouldn't say it was really portable.  It would have helped had I notched some more of the wood out of the 2x's.

It is important to get the slope right and it will surprise you how long the mound needs to be to accomplish this.

I definitely agree with what adbono is saying about having the kid taking ownership but not sure how many would put it together well enough.  At least make them part of the process at least for sure.

Built one very similar to the one Good Knight referenced.  It's lasted almost 8 years.  I painted the surface to keep it from soaking in the rain.  I also put down gravel to keep the wood from touching ground and allowing the area to stay dry.  Two or three of us could move it but it was heavy.

At one pitching facility, they built the base without the plywood and filled it with dirt to create a more natural mound.  It required regular maintenance but it was really nice.

Have built multiple ones.  Cost about $150 (maybe more now with the cost of lumber going sky high)  4- 2X10X10, 2 sheets of thick plywood (the thicker the better), screws, and carpet (does not have to be green or indoor outdoor)   Buy a large tarp and wrap it every time when done and it will last forever.  I also have plans for a portable one that one person can carry.  A little more complicated but you can take it to softball field and throw.

Lefty built one with assist from dad during covid.  Used same general idea as above.  Used 3 2x10x10 and it feels sturdy, even with 200lb plus kids on it, key is to use think plywood.  Painted the base to help with the waterproofing (we rarely move it).  Initally was going to use horse stall mats but realized in CA they would get hot very easily, opted for the indoor/outdoor green "turf"like carpet from Home Depot, it's broken down some with use, really the only part of it showing any wear and tear.

If the mound is going to stay outside using pressure treated lumber to build the base will extend the life. Another option for an outside mound is to build a 3 sided frame using pressure treated lumber and fill the interior part (the mound surface) with decomposed granite. It creates a solid base that won’t erode and is unaffected by  water. However, its a little hard on cleats and tends to wear them out for guys that have a lot of toe drag. Tuff Toe makes a product (in many colors) that is a paint on epoxy to create a tougher to harm surface on the area of the shoe that drags the mound.