There have been a few on kids footwear - I’ve worked with one of them in the past and am working with another one now.
Depends what you define as successful, one of the brands I worked with had only failed due to a big falling out that was nothing to do with the product - we had lots of orders when it went under.
The footwear company Nat-2 from Germany does the most interesting ones (IMO) every season they seem to move the concept on a little. Their hero product is a sandal which becomes a sneaker.
Seems to work better as casual lifestyle rather than technical.