I'm polish and "a" is strongly connected with feminine nouns and names. The same in spanish I learned for a while... It's driving me crazy. "A" is a woman for me :) When I make a conscious effort I can remember it's the other way round here, but I keep making the same mistake if I do the excercises here too fast.
Nope, Swedish doesn't have that construction. That means that it is a little cumbersome to stress that something is an ongoing action in Swedish. The workaround is to say your body position and the verb and it will somehow clarify that the action is ongoing. For example you cound say Pojken och flickan sitter och äter.
In English, you could say either "they eat" or "they are eating". The latter is called the continuous, because it's something that's currently happening.
But Swedish doesn't have a continuous - we don't make this distinction. We only have de äter. So "they eat" and "they are eating" both translate to de äter.
In English the verb gets the -s ending in the present for he, she, it, i.e. third person singular. So it would be The girl eats cheese.
But when you say the boy and the girl, they become a unit so together they are "they" which is third person plural, and then it has to be The boy and the girl eat cheese just like in They eat cheese.