Creating handheld video games(odd question)

Alright well I was just thinking to myself a bit ago about some things. Some things I was wondering were what language do they create those small little handheld games in? Games like handheld poker, handheld soliate, etc. Also those small little mcdonalds video game toys with happy meals. I know there isn't much to these games, but how do they get the game on the small little 'board' inside of the plastic game? I wouldn't imagine it is hard since they produce these in such high amounts.

If you guys understood my questions that is great, but I know it may be a little odd (Google brought me not much results). I am not interested in creating games like this but I have been wanting to know for a long time.

If this is in the wrong section please move it, I didn't know which board to post it in.