Hi Marius,
A little bit of childishness is an essential for any photographer. Young children are always looking at the world with fresh eyes, and always questioning what they see, and that's what every photographer should be doing, too - whether they're in advertising or in photojournalism. The best photographers are those who see the important things which most of us walk past.
Now that childishness can also help you take an idea and give it that extra nudge it needs to really start getting people's attention - like adding some extra helium to this kid's diet! (Or as we have done here… just extend the canvas and added some more blue sky!)
About my only complaint withthis image is that I wish the kid had lifted his head up into the light as the photo was being made… and removed the cap. Because of the cap and the low head, we have a rather dark spot for a head instead, and it doesn't reveal much of the excitement.
Otherwise… keep inhaling the childishness, I say!
Cheers, Anthony
Image Doctor's edited version