the soft sign indicates softening (palatalization) of a consonant if it is not followed by a vowel. So not only л and ч, but most of the cases: Мальта (Malta), семь (seven), меньше (less), соль (salt). Note however that нч does not allow a soft sign: пончик (donut, pronounced also with a soft нь).
So in english a man can still be a boy, is this the same in Russian? Or would you be looked at oddly. As an example with a young child you might say "Dad is a boy, mom is a girl". Would "Папа мальчик, мама девочка" sound alright? What about an older person saying "Я мальчик" or "я девочка" or are these specifically reference young children?