Stereognosis - the ability to perceive and recognise the form of an object in the absence of visual and auditory information, by using tactile information to provide cues from texture, size, spatial properties, and temperature, etc.

The Mystery Bag (3-6 years) from How to Raise an Amazing Child the Montessori Way; 

The mystery bag has long been a favourite children's activity. Usually it is simply a cloth bag or box with a hole for your child's hands, through which she can touch and manipulate objects that she cannot see. To play you will need a collection of small object with which your child is familiar and which she can name. While she closes her eyes, place an object inside the bag and challenge her to identify it by touch alone. If your child guesses correctly, you and your child switch roles. Keep this game going for older children by making it more difficult, using different coins, shells, or geometric shapes, for example.

I love to use a mystery or stereognostic bag with toddlers. The toddler may take a while to work out how to do it, and they may occasionally take a peek inside the bag but it is a lot of fun. The key to using this with a toddler is to start with only a few items and build up, we started with three, and only use items the child knows the name of. We use a lot of items which are Otto's favourites like the cat, tractor, keys and (hair) brush. We also take turns, he loves to put objects in the bag for me to identify!!

Using the mystery bag of stereognostic bag the child uses only their sense of touch to identify the objects. As the child touches the object they form a picture of it in their mind - this picture builds as the information increases until they get to the point where they can identify the object, without the sense of sight. I can see how Otto feels each object and how he yells or shouts in delight as he names the items and pulls them out of the bag. 

Here are a few examples that we have been using (at 24 months). 

Nature - feather, shell, pinecone.

Model Vehicles - bus, tractor, truck.

Nature - dried leaf, seed, pinecone.

Model Animals - pig, cow, cat.

Fruit and Vegetables - orange, onion, apple.

Household Items - hair brush, torch, keys.

Kitchen Items - fork, knife, spoon.

Toys and Household Objects - block, book, metal stacking cup.

Household Items - pencil, peg, scissors (round tip).