One way they interact with each other is through play. This can also occur when they 'gather around the console' to work together on a problem solving adventure like The Legend of Zelda . I've observed that playing games like this stimulates kids' group imagination, and spills over into activities that they invent away from the console or computer. There are various edutainment titles, in which children take turns or compete, for example I Love Spelling and Math Arena . This is also beneficial as it leads to peer interaction, either helping each other, simply discussing what they like and don't like in the game, or sharing how they feel about its challenges.
Kids can also develop interpersonal skills by example.
LEGO Friends shows kids interacting with each other in different scenarios, chatting with each other, learning to get along and to compromise. They can learn from this, though not as much as from direct personal experience. While a real pet is better, these programs do encourage empathy. So encourage the kids to play with friends on or off the computer and provide them with good role models. Talk to them about feelings and how to read them in other people.