To me "ihm" sounds better, but language use is changing.

Hello Wenky, you are exactly right with your assumption. Although grammatically 'ihm' is correct, native speakers would probably rather use 'ihr', it does somehow sound much more natural although it is technically wrong. (By the way did you know that the reason that 'das Mädchen - the GIRL' is neuter in german is because it is a diminutive form of the old fashioned german word 'die Maid' (maiden, farmgirl, maid). The diminutive of a noun is formed by adding a '-chen' or '-lein' ending to the word, and all diminutives are always neuter no matter what the gender of the root word is. The original word maid isn't used much anymore in modern german but the diminutive has become the modern word for girl. Since english doesn't have a diminutive here's a link to the wikipedia article: https://en.wikipedia.org/wiki/Diminutive. The diminutive basically is just a way of making any noun sound kinda small and cute.)

I as a native speaker would say "ihm" is wrong and "ihr" is right. :) You have to use "ihm" for "dem Jungen"