Even in clear weather if he got icy paws I'd keep him in.

I'm letting my kittens (6 months old) out now for the first time but
only with me present, i.e. I do a couple of hours' gardening in the
afternoon and they play vaguely within my vicinity.

What I would like to add is this. When I go out now (late January) and
start picking weeds etc my hands almost "freeze" but this feeling only
lasts for about 15 minutes: the exertion of physical work, exercise, and
play outside warms you up and very soon you don't feel anything. I
think this is the same with the cats. If they just stood and watched me
they would get a chill. But, of course, they don't: they're flying all
over the place and when we go in at 5, for their tea, they are
exhilarated, with no sign of shudders or being out of sorts.

Nell.