Let me put it this way: You are very lucky. One of three things could have gone wrong:
a) Kid breathes in, sucks flame into his lungs. So, he gets poisonous chemicals + lung burn. BAD
b) Kid turns and looks at you just as you light up. Burnt eyes. BAD
c) Flame follows back into your can & explodes. BAD
---You really didn't consider any of those possibilities before trying this? It's just, from what I was reading, you were lucky the only thing he lost was his hair. a, b, or c and I'm betting there would have been trouble. Although I can imagine by now that c) would be the only one that would affect your attitude. 
Well, I would kinda hope you'd be upset if the kid burned his lungs or his eyes & had to go to the hospital...
Thank you for that wonderful insight into mathematical probability, biology and the dynamics of a gaseous combustion fire - undoubtedly gleaned from snippets of vague technical and scientific information present in ER and Rescue Me (and probably the finale of Enterprise where Tuckers get his lungs burned out).
Firstly, reaction tmie is paramount. The flame was (aside from being nowhere near his mouth of nose) not active long enough for the heat to register as a danger, the kid to wake up, realise what was happening and gasp to a sufficient degree to draw air into his lungs.
Secondly, even if he had somehow managed to breath it in, it's a rapid gaseous combustion. Either the fuel or the air would've burned out too quickly to transfer anything approaching a dangerous level of heat into his tissue, and at worst would've left him coughing for an hour.
Thirdly, the aerosol is not posonous, and the by-products of it's burning are only very mildly toxic. If it were poisonous, everyone would die every time they used a can of deodorant.
Fourthly, the flame cannot blow back into the can due to the size of the nozzle and the fact that the jet of flammable liqui-gas is vacating the can so fast as to prevent a sustainable flame - thus the need to keep the lighter lit and in the stream. And even if the flame were to trace back to the source, you still have a half a second at least to notice the nozzle is on fire and blow it out. And all this is even assuming the contents of the can are combustible in and of themselves, lacking atmospheric oxygen to react with.
Fifthly, as for the 'burnt eyes' scenario - the flame would take at least a full half-second of constant, direct contact with the kid's eyes to heat them enough to cause any damage. At worst he'd get sore eyes from the mild warming and remnant chemicals which failed to burn off.
In short: FAIL!
