I know what you're saying, and the funny thing is that when I wrote that, I actually paused and thought about the proper way of referring to LEGO. So if you google "playing with legos" there's a ton of articles that use that expression, such as this one on HuffPost for example: http://www.huffingtonpost.com/2014/01/28/google-legos_n_4681...

So kids 'playing with their legos' is valid given the fact that LEGO has become a household name and LEGO can refer to the brand, the game itself, while Legos, or legos can refer to the LEGO blocks themselves. It's sort of like using Google as a verb (http://en.wikipedia.org/wiki/Google_(verb))

Thanks for reading btw

PS. English is my third language so a grammatical error here and there wouldn't be that bad anyways :)