Thanks to Snoopdog, are you sure they don't sting, I have small grand children one of which is allergic to lots of things?

I would love to leave them alone..

This is common after scarifying, and not harmful. They will almost disappear next time you mow.

Hi, welcome to GoY, it looks as though you have 1 of over 1300 species of mining bees, that have been hibernating in your garden, 1 of the most common is the tawny mining bee, Andrena fulva, females are a redish orange colour, black underneath, males are a duller colour and smaller, adults emerge from hibernation in spring, they're solitary bees, and rarely, if ever, sting, cause no damage to soil or gardens, and are useful pollinators, the tunnels in which they hibernate are between 8 and 16" deep, and the soil that is excavated is taken to the entrance, which is what you're seeing, and the entrance hole is about the size of a ten pence piece, Derek.

Bees don't sting for no apparent reason as wasps will do in autumn. When a bee stings it then dies so it is not in their interest to attack first. So teach the children to look and not touch either the bees or the mound..