The infiltration (first book)

In a dystopian society of the future...
The year is 2140 and aliens have infiltrated and taken over earth. Out of the previous 10 billion humans, under three million have survived. The remaining government has united and decided to set up Rebel camps throughout the world.
Lee is a 12 year old boy. He lives in an underground rebel camp and is considered one of the weakest in the camp. Seven years ago, his life consisted of sitting next to the main laundromat, accepting food, and begging for units. Luckily a girl changed his life.
Chrystalline is a 12 year old girl. She lives in the same underground base as Lee. She works a decent job as a restaurant worker and has always given food and units to Lee. Lee changed her life in more ways than she could have described. Without him she wouldn't half of who she was...
Zachary is a 12 year old boy. He is one of the nerdiest children in the base. He works in the technological industry and is always busy coding. He lives a straight forward life and has always supported Lee. The adults all praise him, but he doesn't have many friends other than Lee and Chrystalline.
The world as the children know it is coming to an end. The base has intercepted a signal that tells of the aliens master Agenda. It doesn't look good for the human race...