Hi, as others have said, as Shetlands are just mini horses, same as a horse basically. Obviously exercise etc will be different, unless there are some good very small riders around. You won't really need breed specific info on how to care for them or what equipment you need.
So... for eg. they will still need around 2%bwt daily in forage, but as with big 'easy keepers', you will likely need to use a slow feed haynet, muzzle for grazing, ensure grass/hay's not high sugar, or soak the hay before feeding to leach out some of the sugars. I highly doubt you'd ever need anything remotely 'high octane' for them, such as grain, but I do think appropriate nutritional supplementation is important. As with big horses, they're also herd animals, need company. If 2 aren't an option though, you can always pair one with a sheep, goat(to eat blackberries!) or such.
If you're thinking of getting one as a pet, great. But if wanting riding animals for your kids, they may not be too big for one now, but even if they're little, at 6 & 7yo, they will outgrow a shetland very quickly. Whereas a bigger pony - welsh mountain for eg - who is around 12hh should be able to carry small boys for a fair few more years at least. My 12yo daughter is sadly just about outgrown her 12hh pony now...
Blueberry & blackberry. No idea about blueberry, but I'd guess not. Horses love blackberries though, enough to brave some thorns generally. Not sure how noxious & prolific they are wherever you're from, but I wouldn't be leaving blackberries in for the sake of a treat for a short spell each year.... altho I do make the most of other properties where they are, & take an icecream bucket and my horse... Takes a while to fill, counting "one for me, one for you, one for the pot"