God is a complex character to understand, even for adults. Kids should be taught about God in a simple way first so they can grasp who He is and what His presence means for them in their lives. Then, when the kids are ready to ask questions and learn more, you can go into more detail.
Begin with explaining to the children what love is. Use their parents as an example, and let them tell you how they know their parents love them. Then bring in the concept of God as a loving being who looks after them and wants the best for them, just like their parents.
Explain to the kids that there is a difference between God and their parents. This is that God is everywhere and they can't see him. Describe God as a person, but not a real-life, flesh-and-blood person.
Let them know that God is everywhere. This can be a tough concept for children to grasp, but a useful analogy is to compare God to the wind, because they can't see wind but they know it is there.
Let the children draw their view of their family and of God on a piece of paper. If the kids ask what God looks like, you can tell them that nobody knows what he looks like and that they can draw Him as they think He should look.
Give the kids examples of how God works in everyday life. For example, you could tell them that God is the person who created animals and plants or you could tell them that God made each child the way that he is. Allow the kids to draw more pictures of the things that God is responsible for, so they can get an idea of the effect that He has had on the world.
Tell kids they can pray to God for guidance and help in their lives. If the kids ask if God answers all prayers, you can tell them that God helps people to choose the right path and sometimes that the right path is not necessarily what the child prayed for. This will teach them that God is there to help them but also that he is omnipotent and needs to keep an eye on a bigger agenda.
Add to the kid's understanding of God by reminding them that God keeps an eye on wrongdoing. They can then draw a picture of God frowning when a child does a bad deed and smiling when a child does something nice.
Tell the kids stories of God's capabilities, so they can grasp how powerful He truly is and become more familiar with the holy book of your religion.
Answer the kids' questions about God. This concept of an almighty being may be fascinating to them and if you answer their questions they will become more comfortable with Him and His place in their life.
Teach the children a song about God that you feel is suitable for their age group. This way the explanation of God ends on a high note and allows the kids to indulge their playful side while learning about a serious subject.