Have you ever heard someone express the idea that it doesnít matter so much if they prepare too much because they feel if they are over-prepared that they wonít be as open to God leading them during the teaching? Usually it is just an excuse for poor preparation. Thorough preparation doesnít exclude God from the teaching - as long as God is in the preparation. Donít be afraid to even write out your lesson word for word (it doesnít mean you will teach from the script.) Just be sure that God is first, central and last in your preparation.
First of all, before you even open your Bible to prepare, pray. Ask God to open your eyes to something new and exciting that you have never seen before in His Word that you can obediently apply to your life and then enthusiastically teach the children. Ask Him to make you more Christ-like so you will be the lesson the children learn.
Next, keep His Word central. Prepare from the Bible, not the teacherís manual. Plan to keep it prominent in everything you do during the teaching time. Let the children see you holding Godís Word and reading from it as you teach. Godís Word will always point to God Himself.
Lastly, pray, thanking God for the privilege of teaching His Word to the children. Pray by name for the children you will teach. The world, the flesh and the devil will certainly fight to keep the children from putting to practice what God desires to result in His glory.