Read with them.
Tell family stories.
Limit their television watching.
Have books and other reading materials in the house.
Look up words in the dictionary with them.
Encourage them to use an encyclopedia.
Share favorite poems and songs with them.
Take them to the library--get them their own library cards.
Take them to museums and historical sites, when possible.
Discuss the daily news with them.
Go exploring with them and learn about plants, animals, and local geography.
Find a quiet place for them to study.
Review their homework.
Meet with their teachers.
Do you have other ideas?