If your kids are studying Spanish at school and want some extra practice, or if you're looking for sites to support your home-schooling lessons, try these. The sites are all aimed at kids in the 11+ age range, but can often be useful for older beginners too.
Languages Online is a super site, mainly intended for 11-18s, but also very useful for adult beginners. It starts from zero and has a step by step, graded approach which gives plenty of practice of one thing before moving on to the next. The activities for the 11-14 age group are intended to supplement the Caminos series of coursebooks but can also be used independently. The site is not particularly flashy, but it's well-organised and easy to use, and in terms of content definitely gets a five-star rating.
La Tienda de Luis is a Spanish course aimed at 9-12 year olds which can be found on Teachers' TV. (Only available in the UK.)
The same publishers produce Realidades, which follows a similar scheme. Levels A and B are specifically designed for younger learners in this age-group, after which they can pass straight to levels 2 and then 3. Older learners starting from scratch can start at level 1.
The Channel Four website offers Homework High, a service where kids of 11-19 can ask questions about Spanish and get an answer from a teacher. Useful for home-schooling parents too, if you've got a doubt.