1. Teach your children the stories of the Bible and lives of the Saints. We had a 30 minute drive to church and I would tell the Bible stories in the car. Oral story telling can be more powerful than just reading.
2. Say prayers at home with your children. A regular routine of short prayers and kissing the family icons becomes a lifelong habit.
3. Celebrate their patron saints day in a special way. It need not be with gifts, but attend church if possible, make a gift to the church of money, candles, incense, wine or oil (check with priest to see what can be used) or bring flowers. If you can't get to church, decorate the saint's icon at home and light a candle or oil lamp. These are things the kids can learn to do themselves.
4. Live an Orthodox life yourself and teach by example. Orthodoxy need not be just a set of oppressive rules. Your kids need to see that attending church on Sunday and feasts is more important than sleeping in, sports or entertainment.
5. Find ways for the children to participate at church services. Having something to do keeps them from getting bored. Bible story picture books for the little ones; teach them to follow the service books when they begin to read and sing along and cross themselves where appropriate; tend candles or serve as an acolyte when they get older.