Can someone explain the rules on transforming simple to compound and simple to complex sentences for a 10-year-old?
A simple sentence contains a subject and a verb. The simplest sentence would be:
Stop. Subject (understood "You"), Verb, stop.
Other examples include: I will go.
You and she will visit me.
A compound sentence has two complete sentences joined by a conjunction. Two complete sentences which are related may also be joined by just a semicolon.
Ex. You will go, and he will stay.
Mother went to the store; she bought milk, eggs, and bread.
A complex sentence has one complete sentence and one dependent clause (it has a subject and verb, but can not stand by itself or make sense by itself).
Ex. When I was young (dependent clause), I used to fingerpaint.
The girls talked of Justin while he was listening. (Boldface section is the dependent clause).
A compound complex sentence is a combination of the above two--it has two or more independent clauses and one or more dependent clauses.
Ex. While we were in school, my father came to my house and my mother planned for us all to go to Disney for Spring Break. (bold is dependent clause. Italics is the first independent clause. Regular type is the other independent clause).