Kids learn by seeing and doing.
You teach by doing and letting them see.
If you want them to learn prayers, you pray with them, learning as you go if necessary. My youngest (2.5 years) can lead the Hail Mary, the Glory Be, the Our Father and knows most of the Apostle's Creed by sitting on my knee when we say rosary out loud as a family. My 8-year-old actually knows the Mysteries better than me! If you're not sure how to do it, there's little booklets that break it down for you. We do only 1 decade with our littlest ones. We light a candle when we pray to make it special and it helps them pay attention.
You go to Confession and make a full Confession if you haven't already. Wipe the slate clean and get the graces you'll need.
You go to Mass with him. You don't use the crying room, but you get excited about what you see up front. Get a little missal that explains the parts of the Mass and the prayers/reading to follow along with. You teach him that the host is really Jesus. You show him how to use the Holy Water to bless himself (and watch he doesn't use the toilet to practice at home...
). You encourage him to genuflect and make the sign of the cross at appropriate times.
You pick up a few books about the faith so you yourself understand it and can explain it to them. A Baltimore Catechism (get a level 0 or level 1 if you really need a refresher) is a great place to start
You get some picture books to read with him that talks about the faith. Read picture books that embue the values you want to impart. Message me if you want a list for what we like to use.
Expose them to the music. There's tons a great kids music out there.
Choose 1 or 2 things to do, and start there. Maybe it's saying the Hail Mary, the Our Father and the Glory Be at bed each night. Maybe it's saying grace. Maybe it's getting a picture of Jesus and putting it on your wall and talk to him with your child each day. Maybe it's saying the Angelus at noon.
Your child will lead where ever you follow. Decide where you want to go, and start walking there.