They are not baby composting worms as these are the same colour as the worms, only smaller. Instead, they are a harmless parasite called entrachyadid. Most worm composting systems have them.
However,they are more able to withstand wet and acid conditions than your standard Wigglers so, if they seem to be growing in numbers, check that the bin is not waterlogged and mix in a little Lime Mix to increase the pH. They can often be lured onto a piece of moist bread for easy removal.
They make a great treat for your garden birds!