Noddy Fun Time is a nicely-designed and fun site from the UK that would be great for early learners.
The five activities on the site can be used to target basic concepts and categories:
Pop Pop Balloons- choose a balloon color and shape and hold down the mouse to blow it up. The longer you hold, the larger the balloon will be.
Tessie's Garden- Plant seeds of various kinds and create patterns in a garden. Water them to watch them grow.
Magic Mazes- Drive a car up/down/left/right in a path to collect "parcels"
Rainbow Maker- Mix colors together to make your own customized rainbow.