The subject of the sentence is who or what the sentence is about. If there is an action verb, the subject of the sentence is usually what is doing the action. This sentence is all about the children and the adults. They are the ones that are preparing.
2. prepare
The simple predicate is the verb phrase in the sentence. In this sentence the verb is an action: something you can do. The verb is prepare so that is the simple predicate.
3. prepare for the holiday by decorating their homes with symbols of springtime.
The complete predicate contains the verb and all of the other information that comes after it.
knowlegde is more stating facts, understanding is the reasoning behind the knowledge its what helps it make sense. it is saying that we have knowledge, but we dont understand the reasoning behind it