Agree the internet, books, vids, are great! But don't just do that! There is no comparison with hands-on lessons. Have you got any experienced horsepeople around you that you can enlist? Trainers, breeders, etc you could ask? The vets might be the best bet for telling you of good people in your area if you don't know of anyone.
Perhaps I've got it wrong, but it sounds like you are saying you're very inexperienced & don't know much about horses, but have 2 youngsters - one very young, and need to know... everything!
No 1 start with basic care. Hay or grass, water and a secure area with shelter are of course basic necessities, but learning about correct feeding & nutrition is important. Good nutrition, especially for growing youngsters is vital for a healthy, strong horse.
Exercise/free movement on firm ground is important and especially if the horse is cooped up, alone or otherwise unmotivated to exercise a lot at home, taking them out for walks & some trotting or such is important, not just for developing bodies but developing strong hooves too.
Finding a good farrier and vet is very high on the agenda. The vet for emergencies of course, but for routine shots etc that may be required, and you might get the vet rather than a horse dentist to do the yearly(on av - more often for youngsters) maintenance that they require. Farriery is needed about every 6 weeks to maintain hooves.
Horses need to be trained to pick up their hooves & accept hoofcare, and it is especially important that this is not done forcefully with youngsters, who's bones & joints can easily be damaged with rough handling. I definitely advise hands on instruction for that, as not only is it dangerous but it's very easy to inadvertently teach the horse the wrong things, cause them to be worse, more dangerous with their hooves in future. It's not a farrier's job to teach your horse... or to have to deal with dangerous animals, so if that happens, you may find no farrier wants to go near your horse - neglected hooves and lameness result... But maybe, if no one else to teach the horse & yourself, you could ask a farrier for some instruction sessions.
I agree with others, that while it does depend on type of horse(eg Haflingers may be small, but strong, stocky) and of course the size of your son - he may be a jockey! But generally speaking, a 16yo boy is way too big for a 12hh pony. And a horse that is only 2yo is also still very immature physically, skeletally, so I would be hesitant to do much at all of any riding yet, even with a small rider.
The other thing about your son riding a 2yo is, assuming the horse was correctly trained in the first place, he will still be extremely 'green', only know the basics & not so solid in even them yet. And assuming your son is far from an experienced rider & trainer, that's setting them both up for problems - the blind leading the blind... which can be very dangerous for the rider too! A good teacher - trainer/instructor would be invaluable. But for your son, some lessons too on a well trained horse, especially if he's also a beginner, and leaving his pony to grow up & receive more training in the meantime is what I'd strongly suggest.
Oh & while there may be 'quarantining' or such to consider, keep the horses together asap, so they can be horses together, find security in eachother. And hopefully if the 2yo was well 'socialised' with other horses before you got him, he will also teach the baby, where the mum left off, some 'horsey manners'.
Last edited by loosie; 11-25-2015 at 08:56 PM.