Disclaimer: I’m not a qualified physical therapist and the content of this post is based on my own thoughts and experiences.
Firstly, let’s take as an example stereognosis. Have a few common objects and start by showing your child the common objects and then the cloth that you will use for a blindfold. Explain who blind people are and then show your child how to fold up the cloth so it can serve as a blindfold. Then explain that after you tie it over your eyes you will not be able to see. Blindfold yourself, and ask your child to give you an object and explain that because you can’t see you need to feel it in order to guess what it is. Then as you feel and identify the object explain how you know what it is.
Now sit your child on your knee and say that you are going to blindfold them and that they won’t be able to see. Explain that being blindfolded is nothing to be scared of when you’re safe with mummy but if they do get frightened you will remove the blindfold.
Start with a common object, like a soft toy. Another suggestion could be if your child has more than one soft toy, can they feel the differences blindfolded. See: https://www.youtube.com/watch?v=sfifosSms1A
If your child to prone to losing a cuddly object in bed at night and cries for it, blindfold your child in the day time on their bed and have them feel around for objects. Try making noises in the room like opening windows or things like that and have them identify the noises. This might prevent them from becoming scared when they hear strange noises at night.
Create a positive association to blindfolds by linking it with cuddles and sleep. Help them become comfortable wearing a sleepmask in bed to help with sleep, so you might want to get a child size sleep mask. Try dreamessentials, a sensory toys shop, a Montessori shop or www.teaching.com.au