I always have a pack of rich tea/digestive biscuits along with some icing sugar & sprinkles in the cupboard.
Either make up a plain white icing using the icing sugar & water or add food colouring to make different colours. Decorate using sprinkles, marshmallows, sweets, grated chocolate & anything else you can think of. Great fun to decorate & then eat.
Once weaned, babies can explore the icing & it’s all edible too.