I've only read the first two pages. I've come across a handful of errors already, so I'm going to stop. Before I start, I will say that this is not entirely bad, and if you fix these problems, it will be mich nicer to read, allowing us to look more closely at the story ans the dialogue.
Your second sentence starts 'You can see...'. We don't use that sort of language in screenplays. You need to show what the reader is seeing (describe the scene), not tell them.
Name the family members straight away. Even the boys. The mother is suddenly named on page 2, only when she speaks. She needs to be named in the action before this.
Also, add descriptors for each character. Right now I don't know how old BOY is. Based on his dialogue, I'm guessing he's a toddler, as he can't talk properly and repeats the words of others. Is that correct? Or is he retarded? Actually, they both sound the same. Are BOY and BOY 2 getting mixes up???
'Jack*has*combust*a*fire*within*a*pile*of*wood*which*is surrounded*by*rocks.*The*flames*scatter*as*they*look*at*it*with*amazement.' - Simplify thing like this. A fire within a pile of wood which is surrounded by rocks is actually just a campfire. And then, how do we know Jack built it? We don't. It's just there. And who are 'They'? You need to show us.
No, you shouldn't show Jack building the fire. But you also shouldn't write 'Jack has built a fire' if you can show that Jack has built a fire. How will the viewer of the finished film know that Jack built the fire? Does it have his name on it?