How do your children learn to pray?
They listen to you. That’s how they learn anything, to begin with.
So, do you pray out loud with your children, letting them hear you using your own words to speak to God? When you gather before your home altar, don’t just use pre-written prayers, lovely and worthy though they are! Begin (or end) with a prayer that comes from your own heart, clothed in your own words, coming from your own thoughts and for your family’s current intentions. Praying spontaneously like this models your relationship with God for your children: it gives them a sense of what words to use when they pray.
I first realized the importance of modeling prayer a few years after I had started teaching Sunday School at my parish. With a room full of third-graders, many of whom barely knew the basics of the Faith, I saw that it was important to give them the words to pray, to give them a model to imitate and follow for their own prayer life. My prayers were simple, and I repeated myself a thousand times; I stumbled awkwardly and nervously sometimes, but I still prayed with them and for them each week and for the intentions they asked me to pray for. They heard me pray spontaneously each week, and then they all joined in at the end with the Divine Praises which we recited together. Sadly I do not have any data or anecdotes to know if any of my students were able to approach God in prayer more easily after hearing me pray for a year in my class, but I do know that this was something that had helped me in my family when I was young, and hearing adults praying had shaped my prayer life. This was another tool that had been given to me at home, and I wanted to pass it on to these young ones in hopes that it would bear fruit one day.
Praying out loud before your children also teaches them about the different kinds of prayer there are: for example, all children understand that they should ask God for what they need, but there are other forms of prayer than “petition.” They will also learn from hearing you pray how to express sorrow for sins, how to praise God’s majesty, and how to make a prayer of thanksgiving for blessings received. (If you are not familiar with these different kinds of prayer, do a little reading up on prayers of contrition, adoration, and thanksgiving. Dr. Peter Kreeft has written good books on prayer that I recommend!)
Don’t be afraid, and don’t overthink this–just get started. Pray out loud, so that you can help God shape your children’s interior life of prayer.