Eating can involve all the senses when we really pay attention, and mindful eating simply involves deliberately noticing the food in relation to all the senses.
Give the child something to eat (at my daughter's nursery, it was a large rice cake), and start by asking them to take a good look at it. Then ask them to sniff it and notice how it smells. How does it feel in their hands, and what is its texture like? Then when they take a bite, ask them how it feels in their mouth. My daughter and her classmates would then place their hands over their ears and listen to the sound their mouths made as they chewed.
This slows down the eating process (an added bonus of being good for digestion!), helps children pay attention to all the signals their body is providing, and shows them how many ways they can enjoy food.