The Learning Planet website has a big collection of games for students, categorized by grade level. The preschool and kindergarten section features six games that teach essential skills to young children. Choose from an alphabet game or two different counting games, or play "Mr. E's Matching Game" to practice memory. The site also has a time-telling game to help kids practice rudimentary time skills (by labeling the numbers on the clock).
The Kinderweb site is specifically designed for preschool- and kindergarten-level activities. The 13 games on the site teach children letters, numbers, colors, shapes and animals, as basics. There are more advanced games for quick learners, including time-telling activities, basic math skills (like adding and subtracting) and currency games. Kinderweb also has printables related to the games for coloring.
What Kindersite lacks in organization, it makes up for in volume. The games here are sorted alphabetically, which isn't very helpful for picking out games related to specific themes, but after taking some time to try a few out, you'll spend hours playing with your kids. This site collects games from a variety of sites and links to over 200 games. Games are listed with an appropriate age beside them and the original publisher in brackets, so if you like a particular game, you can visit the publisher's website to see if they make similar ones. There are even a handful of basic Spanish games for young learners on Kindersite.
The EZ School education portal has games for students from preschool through the end of high school. Games for younger children are categorized in the "Preschool - Grade 2" section and then divided into two subcategories: English games and math games. Some of the math games may be too advanced for children aged five and under, but a lot of the English games teach phonics basics and key reading skills. The games have printable tie-ins like flash cards and worksheets to help reinforce the lessons.