It is important to note retailers are not doing anything illegal in selling these Halloween costumes.
The government has ordered Trading Standards to carry out spot checks on costumes to see if they meet safety standards.
But fancy dress outfits are classed as toys to be played with rather than worn - so only have to be tested for lower flammability than say pyjamas or nightwear.
The Channel Mum investigation also found:
Trading Standards said they are currently carrying out an investigation into the safety of Halloween outfits and will publish a report in the autumn.
ITV News has contacted all of the retailers whose products were tested in the Channel Mum video.
An Asda spokesperson said: "We recognise that children’s dress-up costumes are no longer occasional wear, so we’ve introduced more rigorous testing to the same standards as nightwear."
Sainsbury's said: "We are proud to confirm that all children’s dress-up outfits sold in our stores and online from Halloween 2015 meet both European Toy (EN71), and British nightwear flammability (BS5722 test 3) safety standard - the toughest standard that currently exists."
While M&S replied: "We are confident that all our childrenswear meets all the relevant safety regulations and the very high safety standards we set ourselves. Every dress up item is subjected to independent flammability tests under strict laboratory conditions to make sure this is the case."