Without prayer WE will be teaching the class - not God. We must ask the Holy Spirit to work through us - to give us the words, the actions, the silence, whatever is needed to do His will.
LINK: USCCB Catechist Prayer (Printable)
I arrive at class early and spend a few minutes in the chapel, or in the classroom praying. If that's not possible you can pray in the car! Turn the radio off - ask the Holy Spirit to guide you and work through your heart and your hands. Ask Him to give you the words. He will - He never fails! God bless you.