as far as I'm aware, Norwegian doesn't have that kind of conjunction, but the sentence "Gutten leser et brev" can't be "The boy reads a letter" because it wouldn't make sense grammatically as he is reading the letter now. You could say "Gutten leser brev", which would be equivalent to English "The boy reads letters", meaning he generally reads letters, but not necessarily right now Hope it helped:)
"Lad" is a British term identical to "guy, boy" and the application presents you with possible alternative translations once you pass the exercise.
However, it can't be used synonymously with "the child" because it warrants a child of male gender - a.k.a. the boy (who lived).
"The lad/The boy is reading a letter" (correct answers) is not the same as "The child is reading a letter".
There are three genders in Norwegian: masculine, feminine and neuter. Each gender has its own articles.
Masculine: en gutt (a boy), gutten (the boy)
Feminine: ei/en jente (a girl), jenta/jenten (the girl)
Neuter: et hus (a house), huset (the house)
Genders usually don't depend on logic, apart from very basic nouns like man and boy being masculine and woman and girl being feminine, but with most nouns, you just have to learn the articles along with the noun. Also, as you might've noticed, feminine nouns can sometimes take the masculine form, it depends on dialect and personal preference