My 7 year old nephew visits me on almost a daily basis. Usually, he wants to use my computer to play video games. I indulge him and let him play onLog In. At times, he brings a friend with him who is either his age or tops 10 years old. Are there any other sites good for kids under the age of 10?
Let him visit neopets.com. It's like pokemon wherein you get to choose a pet, take care of it, visit different lands, compete with other players, and just have some fun. It's quite enjoyable. If you want a fun and free MMMORPG, go to runescape.com. I think it's the oldest MMORPG available online. It's also the first MMO that I have played. It's simple, addicting, and could be enjoyed by little kids as well.