In a test of the durability of 10 best-selling stair gates, they applied the “fatigue test” - simulating the gate being pulled back and forth by a toddler - 10,000 times.
The test is part of the EU safety standard for safety gates.
Samples of the Dreambaby Retractable Gate, the Lindam Easy Fit Plus Deluxe Safety Gate and the Safetots Self-closing Gate, failed to meet the EU safety standard, Which? said.
It found that the Dreambaby Retractable Gate failed after just 10 applications of force.
Which? said that after just 10 applications of force the metal tube that is attached to the stair gate became bent and started to detach from the casing holding it in place - causing it to sag in the middle.
The Safetots Self Closing Gate failed after 3,700 applications of force, Which? said, with the adhesive pads that secure the gate to the door becoming detached.
It said the problem could lead to the gate becoming loose due to a lack of pressure.
The Lindam Easy Fit Plus Deluxe Safety Gate’s adhesive pads also failed after 2,570 applications of force.
The watchdog has now put all three items on its “don’t buy” list on its website and is calling for an immediate recall of the Dreambaby Retractable Gate.
It said anyone who already owned the gate should stop using it immediately.
Which? recommended that anyone who owns the other two gates should stop using them until a solution to the failure of the adhesive pads has been found.
Alex Neill, Which? managing director of Home Products and Services, said: “It’s shocking that the products people buy to keep their children safe may actually be a danger to them.
“The manufacturers need to act urgently to prevent any more children from being put at risk by products which may be unsafe.”
A spokesman for Dreambaby told Which?: “Complaints relating to the quality of our products are rare but when received they are investigated immediately.
“However, our ability to undertake a thorough investigation of the matters raised have been significantly frustrated by the failure of Which? to provide sufficient background detail despite our repeated requests for this information.
“We are therefore unable to provide a considered response at this time.”
Munchkin, the company that owns Lindam, said it was not aware of any evidence to support Which?’s allegations, and that a review of its customer complaints had not found any issues relating to the alleged safety and reliability issues.
It said its gates were compliant with product safety standards BS EN 1930:2011 - the UK standard for child safety barriers.
Safetots did not give an official reply but said it disputed the findings - it said the gate had been exhaustively tested in China and the UK and met the requirements of BS EN 1930:2011.
Which? said it had reported the findings to Trading Standards and the Office for Product Safety and Standards.