I was reading planet cake and she uses apricot jam to brush on cake layers. Is this the same premise as simple syrup with flavoring? which is better?

It depemds on what she was doing.

Simple syrups can be flavored.  They are meant to soak into a cake and add moisture and flavor(if added) to the cake.

Apricot jam works slightly differently.  It most often used in pastries and cakes to seal the cake or pastry from a moist filling or spread. 

An example is strawberry shortcake.  The juice from the berries is like a simple syrup.  Most people enjoy the syrup soaking into the biscuit.  If you painted the biscuit with apricot jam, the syrup would not be able to soak in as much.

Great thanks. So what can i use for a flavoring; I'm making a kids birthday cake that parents will be eating as well. they want it to be a simple yellow cake vanilla or cream cheese frosting. This sounds so boring to me! what can I use to enhance the flavor? or maybe a sweet whipped cream filling? It will be covered in fondant.

Keep it simple.  An excellent vanilla cake is hard to do.

That said, simple syrups can be flavored in thousands of ways:  coffee, mint, fruit, alcohol etc.  Extracts can be combined to create wonderfully layered flavors. 

However, for a large event, I don't recommend experimenting.  Go with what you know.  Save the experiments for other days.  If it turns out poorly, every birthday people will remind you of THAT cake.
 

The order is for a simple but classic flavor.  It's best to do the order as ordered.