This show's producer, Lauren Faust, felt that the newer generation of viewers deserved more of an actual cartoon with morals and lessons to be learned from it and less of a 22-minute toy commercial like the generations of cartoons before it. In fact, this show—as mentioned by Faust herself—is geared more towards children ages 6-13 and their parents because of the nature of the show itself.
This next paragraph contains possible spoilers.
As to why it scares your children so much... well, several times throughout the show, the 'mane cast' has had to subdue beasts normally portrayed as gruesome and frightening like the mythical manticore (
as seen in Episode 2, 'Elements of Harmony'), the Ursa Minor (
Ep 6, 'Boast Busters'), dragons (
Eps 7, 'Dragonshy' and 24, 'Owl's Well that Ends Well') and the hydra (
Ep 15, 'Feeling Pinkie Keen'). Not to mention it showcases things like death that could easily traumatize someone so young; an example being when Rarity fell from the Cloud-iseum in
'Sonic Rainboom', falling to her doom... though, thankfully, she and three of the Wonderbolts were saved by Rainbow Dash not half a minute later.
This may be advertised as a 'children's cartoon', but your kids are still far too young to fully understand many things this show presents as well as the fact that it is just a cartoon, so it
will either appear to them as either boring or scary. My advice to you—and to other parents that find their children disturbed by this show in some way or another—is to avoid the prime-time 6 PM EST time slot in which this show airs and give your children a few years, until they're either in or bordering on the target demographic. By that time, we can hope that they'll accept this show as the light-hearted cartoon it was meant to be and possibly enjoy it more. Or, if you think your kids might still genuinely enjoy the show, you can sit down and watch it with them; again, this show was also meant to catch the eyes of an adult audience, so your kids might enjoy it more if they see their parents showing a genuine interest in it (
and if you're concerned that you would feel out of place watching and enjoying a show like this, don't be... in fact, if you look closely and carefully, you'll find a great many communities of adult men and women online that fawn over this cartoon).
In summary, just do one of two things: give your children time to learn to enjoy it, or give them incentive to give
My Little Pony: Friendship is Magic a second chance. A good episode to introduce them to is Episode 11,
'Winter Wrap-Up' (
you can view this and many more of the episodes in high quality on YouTube, if you have access to a computer at home.); in addition to being among the tamest of all the episodes and demonstrating the best of the main characters' personalities, it has an amazing musical number that will have anyone singing along to it.