Safety tests found that cartoon-style hats formed a "noose" which would not break under pressure, experts have revealed.
The under-chin ties remained tight even when force was applied, violating legal safety standards and posing a risk of hanging or strangulation.
Almost 100 of the hats were seized from market stalls in Nottinghamshire and a shop in Mansfield, and the county council has issued a warning to traders against stocking them again.
Anyone who spots the hats on sale is urged to report the seller to trading standards immediately.
Children's hats featuring beloved cartoon characters have been taken off the shelves after safety tests found they posed a serious risk of strangulation.
A total of 99 hats, which were being sold by a shop in Mansfield and by two market traders in North Nottinghamshire, have been seized by trading standards officers in the county over safety fears.
Safety tests have now confirmed they are unsafe.
The colourful hats are furry and are styled to look like Hello Kitty, minions from Despicable Me, and other animal characters.
It comes amid renewed interest in a warning over dangerous dolls being sold in the region.
Read: Dangerous Dolls Warning