If you would like to create and send e-cards for special occasions or just to say hello, there are several websites that make it easy.

Animated Cards for Kids

This is a simple e-card engine aimed at younger kids and is part of the larger Up to Ten website, which has other activities, and is bilingual English/French. The e-cards page has a small advertising bar on the left-hand side.

Greeting Island
Offers e-cards and printable cards and is very integrated with Facebook, and probably more attractive to upper-elementary and middle-school ages.

Pitara Kids Network eGreeting
Multi-cultural-focused site for kids under age 13. E-card holidays include a wider range of religions, and the site has several other games and activities.