Hi Chris,
If you are to rebuild the mount into a dobbie style one, look into making it a table top design. The tube of the scope is short enough for it. It can be used on a table, chair, esky, tree stump, really just about anywhere. Will do a few things, make for a very stable mount, bring the scope to your son's height, and its pint size won't intimidate. The current scope my kids have is a little 114mm newt with a 500mm focal length on a table top mount - tubby thing that my kids find
very easy to use. The pic below shows my son with their little scope.
Being only four, your son will also benefit from this table top design. It won't shake as much, especially if he makes a grab for it. Don't be afraid of him grabbing the scope, especially if it's "his". He'll quickly learn how to handle it. Much better than putting "NO" conditions around the scope. With novices, yes it is a good idea to have a no-hands policy, but with your own son/daughter, I'd say the opposite. They won't break it, and the experience will be a better one that will encourage them. Especially with focusing, they'll need to learn to adjust focus for their own eyes. This comes with time too.
In its current state, I'd suggest keeping the tripod as short as possible rather than fully extend its legs. Yes a real pain in the bum for mum and dad, but the scope will be more stable.
Eyepiece wise, I never thought I'd say this, but the good old Kellner 10mm is actually an easy eyepiece for higher magnification in a scope such as yours. For its focal length, the eye lens is big enough, eye relief is surprisingly good, and it certainly won't break the bank. Image quality is surprisingly VERY good for such a modest eyepiece. Kellner eyepieces will have the initial "K" on them. But for some reason I don't understand, many manufacturers call these eyepieces "Super" - not super plossl (which is also a marketing gimick), just plain old "super". But these are still Kellners and just fine for this purpose. Shorter focal length Kellners are also easier to look into than plossl eyepieces of the same focal length.
If your son maintains an interest in astronomy as he gets older, you can then look into a better scope and better eyepieces. Investing in better eyepieces for the modest little scope you have is not worth it. Patience is more important now,
For now, a 25mm plossl and 10mm Kellner is plenty to show the Moon and planets and the brighter deep sky objects.
One trick I have to help little kids look into an eyepiece is quietly say to them "look into the little glass window", pointing to the eye lens of the eyepiece. As most little kiddies are not used to using just one eye to look into a little hole, it also helps to have them hold one eye closed with a hand as they look into the eyepiece with the other eye. They'll get the hang of it quickly. On outreach nights, a step ladder is one thing I also have not only for the kids to access the eyepiece, but for kids to grab the ladder instead of the scope. The ladder I have is similar in design as that posted by Rick,
Chris, if you don't have one of these 10mm Kellner eyepieces, I have one I am happy to send you for the cost of postage. A 25mm and 10mm eyepiece will be plenty to get this little scope for your son up and running nicely. Let me know.
Alex.
I too have such little mementos on some of my stuff. And like you, it's a welcome reminder of my little ones 
