You can easily make your own playdough at home from a few simple (and one harder-to-get) ingredients.  You will probably find that homemade playdough lasts longer than shop bought playdough and you can control the texture a bit better too.
A huge ‘thank-you’ to King’s Oak and their Parent and Toddler Group for sharing their playdough recipe with us!

Basic Playdough Recipe

2 cups plain flour
1 cup salt
2 cups boiling water
4 teaspoons cream of tartar (this is hard to find in the supermarket, but you can order online from Pastai de Vanilie) 2 tablespoons cooking oil

Put your flour, salt, cream of tartar and oil into a large bowl. At this stage you can also scents, essential oils or food essences if you want to make your playdough a smelly sensory experience!
Carefully pour in the boiling water. If you want to colour your playdough (otherwise it will be cream-y in colour from the flour), then add your food colouring to the boiling water (the more colour you add, the stronger the colour of your playdough).
Now mix it quickly with a spoon.
When it has cooled slightly then knead well.

How can my toddler be involved in making playdough?  

They can help you find the ingredients. Measure the dry ingredients and pour them in to the bowl. They can help you count the spoonfuls of oil or cream of tartar.  Please exercise caution around the boiling water and check yourself that the playdough is cool enough for them to then be involved in stirring and kneading it.