Prayer has always been a part of the life of God's people; and as part of the principle from Deuteronomy 6, to teach your children when we lie down, and when we wake, we should be regularly in prayer with them. Prayer is the type of thing that kids get perhaps better than adults. They aren't diverted by imaginary barriers that we older folks have invented by being so wrapped up in ourselves, but rather they know they have full access to God, as we all should know.
But we must model a prayerful life. Pray at meals, pray at bedtime, and if there are urgent matters, as there always are in families, pray about it.
TEACH ME TO PRAY: Read them the story of Paul and Silas in prison, from Acts 16. They were praying and singing hymns, and the prisoners were listening to them, when suddenly a great earthquake came, and everyone's shackles came undone. I won't spoil the end for you, but this is a great example of God's awesome power and the necessity of seeking God's face in prayer.
A good acronym to use in teaching our children to pray is ACTS: Adoration, Confession, Thanksgiving, and Supplication (Asking for things). This helps them to stay focused on all aspects of prayer we see in God's Word: a praising of God, confessing our sins, giving thanks for his grace, and petitioning him for our needs.
QUOTE TO REMEMBER: "The only person who dares wake up a king at 3 am to ask for a glass of water is a child. We have that kind of access." - Tim Keller
GIVE IT LEGS: Make a commitment to pray with your children daily, and not just rote prayers that we often do at meals, but really pray to a God who loves to hear.