Memorize the words of the Lord's Prayer if you don't already know them. The prayer is short and broken down into five different verses. Memorize one at a time until you know the entire thing.
Choose a familiar melody to sing the prayer to, or make up your own tune. For example, you could use the tune of the ABC song or "Twinkle Twinkle Little Star" that your children already know to set the Lord's Prayer to. If you aren't musically inclined or can't get the words to match up with the tune, you can use a version of the Lord's Prayer song as performed by a professional singer or choir.
Teach the words of the Lord's Prayer to your children and sing it to them on a regular basis. Encourage them to sing along.