Little Nightmares II

During Chapter 3: Hospital, you will reach the toy room (just past the X-Ray room). In here, on the shelf grab and equip the teddy bear hat.

Now, take the teddy bear with the key inside (it's the far right one / or use the xray to double check), and carry it down the elevator to the incinerator room. Incinerate the teddy bear while wearing this mask to gain the achievement.

In Chapter 3 (Hospital)

You’ll need to use an x-Ray machine to find a key inside of a teddy bear and bring it down to the incinerator.
In the room where you find the bears there is a Bear hat on the right side on top of the bookshelf. Climb it and equip the hat before you put the bear in the incinerator to unlock the achievement.
Wearing any other hat will not unlock the achievement.

During chapter 3 you'll have to incinerate a teddy to obtain a key, to get the toys are for kids achievement you'll need to wear the teddy bear hat whilst burning the teddy. Here is my own video guide that shows where the teddy hat is and how to get this achievement done along with all of the other achievements Little Nightmares 2 has to offer. This particular achievement is shown at around the 12:30 mark in the video.

In chapter 3, just after passing the x-ray room, obtain the bear hat from the toy room on top of the shelves on the right and press start to equip it. Proceed with the chapter and x-ray the toy to find the one with the key inside then take this down to the incinerator and incinerate it while wearing the bear hat.

C'est au cours de votre passage dans l'hôpital du Chapitre 03 de Little Nightmares 2, que vous pouvez déverrouiller le Succès/Trophée "Les Jouets, un Jeu d'enfants". Commencez par entrer dans la pièce après la salle de radiologie, puis montez sur l'étagère afin de ramasser le Chapeau Ours. Equipez-le avant de récupérer la peluche de lapin au pied de l'étagère, puis revenez sur vos pas pour prendre l'ascenseur qui mène au sous-sol. Jetez alors la peluche dans l'incinérateur, actionnez le levier pour le mettre en route, avant d'entrer à l'intérieur afin de débloquer le Succès/Trophée.

While in the hospital in Chapter 03 of Little Nightmares 2, you can unlock the "Toys Are For Kids" Achievement/Trophy. Start by entering the room past the X-ray room, then go up to the shelf to pick up the Bear Hat. Equip it before retrieving the rabbit stuffed animal from the bottom of the shelf, then retrace your steps to take the elevator to the basement. Throw the stuffed animal into the incinerator, turn on the lever to start it, and then go inside to unlock the Achievement/Trophy.