Could be mealy bugs. (The little hairs are probably air roots, that's ok.) Dip a cotton swab (q-tip) in rubbing alcohol and dot on the fuzz to kill them if that's what it is. Keep an eye on them every day to see if it returns. Are these plants in a terrarium? Terrariums are more appropriate for tropical plants, many kinds of houseplants. If they are in a terrarium, even if it's open, transition them to pots with appropriate soil. This is too humid an environment for succulents, poor air circulation. They store water in their roots and leaves, and wet soil or humid environments is not good for them.

I believe your 1st plant is Anacampseros that naturally has 'fuzz' between the leaves. BUT - there are signs of mealy bugs on it and also on 2nd plant (looks like string of pearls). Treat as socks suggested ASAP. Do not keep any succulents in terrariums pls. Not a good environment for them - there are plenty of different plants that would like that kind of conditions, but not succulents.

Thank you for your advice, I'll get on that asap. I thought terrariums were okay if they were not enclosed as I live in England and humidity is not an issue here. Could you advise what strength rubbing alcohol is needed?

First, I know of no terrariums that have drainage holes, which are an absolute necessity for C&S. And even without being fully closed, they will produce a higher humidity than is desired by these sorts of plants. I'd also question how much light those encased in teal colored glass are really receiving........I doubt it is enough to make them happy.

I have ordered some rubbing alcohol, perlite and some new pots for my plants. Thank you for your help