I have the Ballerina navy and white. Where do I purchase new wheels? The little black plastic knobs are breaking off mine.
Well, just so, nowhere. YOu have to contact the seller of your pram (or any that supplies this Baby Active model) and ask them. They should order the wheel(s) as a spare part (you might be having to pay some fee).
Another way is to contact the manufacturer directly at firstname.lastname@example.org They might (but might not) answer - I can't promise you anything since this is up to them. Often, the cheaper pram manufacturers don't provide spare parts...
I wish you good luck!