I keep my mini mare in with my Appy Gelding in the pastures and they share a run in shed and we had problems before when I also had a mini stallion out there but once he was removed my mini mare and Appy Gelding get along perfectly and it's easy to find them in the pasture by finding the gelding and I know the mare is there close by. Around here I would never keep a mini alone even with another horse nearby, we have WAY too many coydogs and coyotes and Missy, the mini mare, is blind in one eye and 21 years old, she can run and play but run and protect herself against a pack of 6 coydogs? Alone? NO. So keeping them together is making sure that if some coydogs came up they would think twice when they see the large white horse standing with the little gray one. I don't even like keeping her alone in the stall so I have it set up so she can move to her own 'side' with a few boards across and Glyder can't get to that side but she can, but everytime I have been in there they are standing side by side in the same side, usually with Missy Snoring.
Keeping Minis in with another horse is a great way to keep them socialized and get them use to new things. I know I had amish come over and thier horses FREAKED OUT! At the sight of the minis, they had no idea what they were and took off down the drive with thier owners running after them! So it's just another thing to get your horse use to.
Also as for the kids, that's how I learned. My mom gave me 3 minis at once and said if I can keep them healthy and happy for 2 years when I turned 16 I'd get a horse. So I did, you can do just about everything with them that you can with a big one, keeping wieght of the rider in mind. I did not ride them, but I got lessons from a instructor and learned off her pony. But when the time came and I got my first horse, I knew what to do. Minis can be stubborn as well but Minis being bratty is easier than a Thoroughbred or Appy being bratty and with the minis your kids can learn ALOT about horse language and what NOT to do much easier.