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Your local Church should have religious education classes starting as early as kindergarten. Communion usually happens in second grade and some Churches expect your child to have completed two years of religious ed.
If you are lucky enough that your parish offers the Catechesis of the Good Shepherd, I highly recommend it. Level one is offered for children ages 3 to 6. It is a fantastic progam involving an invitation to wonder and and explore God on a spiritual level. They don't use text books. They introduce the life of Jesus directly from the Bible, not a watered-down version. Miniature versions of the altar, chasuble, baptismal font, etc. are used. Dioramas are used as a teching tool as well as matrials for the child to explore and absorb what they have learned. The program is based on the Montessori method. Also, the instructor's personal views or interpretations are discouraged. You can learn about the program by doing a web search.
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