So here's a thought... [S02E13 SPOILERS!]

[Rezo 220]

Considering Pumpkin Cake has intense magical abilities, would she become one of Celestia's "Faithful Students" like Twilight? I mean, Celestia picked Twilight for her advanced magical abilities. And I'm pretty sure Pumpkin can control her magic quite well so far.

[BlazingDawn 52]

Actually, as posted by other ponies, as a very young foal, the magic control is almost non-existent and instinctual. Giving the foal strong magical ability but lack of control, and as the foal gains education, control increases but power lowers.

[cuteycindyhoney 13,307]

I saw nothing comparable to the Godlike powers Twilight displayed when she was startled by the Sonic Rainboom.

[Fizz. 1,078]

http://www.cracked.com/article_18538_5-superpowers-we-all-had-as-babies-according-to-science.html

[Rezo 220]

Actually, as posted by other ponies, as a very young foal, the magic control is almost non-existent and instinctual. Giving the foal strong magical ability but lack of control, and as the foal gains education, control increases but power lowers.

 

Oh, I never knew that their power lowered as they aged.

[BizzarePony 199]

Of course, all of that power is raw and undefined, so the pony's brain will probably subconsciously limit the flow of magic as it grows up to keep itself from being overwhelmed.

[Marshmallow 1,137]

I don't think she actually controlled her magic.

As Rarity said, "Baby unicorns get strange magic surges that come and go."

[Lady Rarity Pony 4,892]

It's a magic surge, she's probably not like that all the time