Children are the best users of magic in the cosmerse

[High prince of geeks]

Since magic in any of the worlds mostly depends on how you think of the magic, Awakening or surgebinding andforgery, or how to use it, Aons and alomancy. If you take a child (8-14) and school them in the magics of the cosmere, while still allowing them to have a vivid imagination they would be nearly unstoppable. Due to the fact of there vivid imagination\ and creativity they would breeze past most problems, of course you'd have to have a more experienced adult nearby to make sure they don't kill themselves. Disagree?

[Tempus]

Magic has limits besides cognitive input.

• If magic only did things when you believe they will happen, no one would have discovered magic because no one would have expected it to happen
• If magic worked only on how you thought it would work, the least skilled people would be the strongest, and would not struggle or overreach themselves as does Vivenna with Awakening.
• Crazy people would be even stronger than kids. So would extremely arrogant people. What would stop an Allomancer from looking at the Lord Ruler and saying "If he can do it, so can I", and then doing it?
• Genetics. If magic happened just because you believed it would, anyone could use magic, and they would all be as strong as they believe themselves to be. There would be no genetic component.

Basically, magic has all sorts of hard limits, and while training your thoughts is important, especially for some forms, it is merely a tool. It is just as important to train your brain to understand how to throw a punch for a boxer, yet a boxer can not throw a megaton punch extending fifteen feet just because he believes he can. You need the knowledge, the muscle, the training, the knowhow just to punch correctly, never mind absurdly. In the same way, the thoughts you use to enact a magic affect the effects of the magic, within the parameters already allowed by the magic.

[Terisen]

There are, as Tempus stated, certain limits to what can be done strictly within the cognitive.  But training children as magic users from the get go might produce better results in the long term than starting later as an adult (I can hear Yoda in my head: "He's too old to begin the training!").

 

I like to think of using magic similar to learning to play a sport or a musical instrument.  Starting earlier in life allows one to "build-in" certain habits that carry on throughout life.  Because of the nature of our brains (here, are crossover between physical and cognitive), we have a harder time learning new things as we get older.  The neural pathways don't develop quite like they used to when we were young.  So a magic user training from childhood might be able to accomplish certain things within the limits set that someone who learned as an adult might not accomplish.

 

Lift's spren Wyndle pretty much said as much when, after stating how he wanted to bond a grandmother but was overruled, said:

 

'She has visited the old magic,' they said.  'Our mother has blessed her,' they said.  'She will be young, and we can mold her,' they said.

 

WoR pg. 684  Emphasis mine

[Swimmingly]

I was thinking it was more like, "We can mold her to fit whatever political purpose we have for her"