This show is perfect for toddlers, it uses repetition to teach animals, colors, counting among other things. The use of repetition is perfect for working with their long term memories as well. My 18 month old and 3 year old both beg to watch Boo! all the time.
I also love how they incorporate tons of different places and locations, its not specific to just Britian.
I doubt I would show this to kids over 4, but I think if you are going to let your kids sit in front of a show, at least let them learn from it. :)