Thanksgiving is a week away, but you can start helping your children understand thankfulness by reading a scripture each day with your family. I prefer doing this at dinner time, and letting my oldest son read the scripture. But you can do it in the car ride home, before your child going to bed, during breakfast or whatever time works best for your family.
Day 1: 1 Chronicles 16:34 ESV
Oh give thanks to the LORD, for he is good; for his steadfast love endures forever!
Day 2: 1 Corinthians 15:56-57 ESV
The sting of death is sin, and the power of sin is the law. But thanks be to God, who gives us the victory through our Lord Jesus Christ.
Day 3: Philippians 4:6 ESV
Do not be anxious about anything, but in everything by prayer and supplication with thanksgiving let your requests be made known to God.
Day 4: Psalm 147:7 ESV
Sing to the LORD with thanksgiving; make melody to our God on the lyre!
Day 5: Psalm 100:4 ESV
Enter his gates with thanksgiving, and his courts with praise! Give thanks to him; bless his name!
Day 6: Psalm 95:2 ESV
Let us come into his presence with thanksgiving; let us make a joyful noise to him with songs of praise!
Day 7: Colossians 3:17 ESV
And whatever you do, in word or deed, do everything in the name of the Lord Jesus, giving thanks to God the Father through him.