"The girls and the boys are reading."
Translation:Dziewczynki i chłopcy czytają.
Frankly... although ""Te dziewczynki i ci chłopcy czytają" should rather be "These girls and these boys are reading", the number of people putting such answers is Too Damn High (c), so they are accepted - after all, in proper context 'the' can be understood as a demonstrative pronoun. The Russian course does exactly the same, for example. But of course I recommend keeping closer to the grammar and translating such sentence simply as perfectly correct "Dziewczynki i chłopcy czytają".
But I was surprised to find that it is one of the two 'best answers'. It shouldn't be, so not it will only be an accepted answer.
'z' doesn't mean 'and. It's main (?) meaning is "with", it can also mean "from" and probably a few other things.
"i" is the normal "and" used for listing things.
"a" is the "and" that shows contrast: "Chłopiec je, a dziewczynka pije" (The boy is eating and the girl is drinking).