My son was bitten last year, and it inflamed into, what looked like a boil. They said it looked to be a spider bite or an insect similar to a spider. Eventually it turned black and later healed, but has left scars the size of a 1p. I did find a spider in his bedding. It was very small and had died. From the underneath it appeared to be jet black.
This year, we have several small spiders in the kitchen. They run away when we are in there, This is a picture of one of them, and I wondered if these can bite?
This one is much smaller and lighter coloured than the one I found last year, but I wondered if they can bite. It seems very odd as we live right up north by the coast, so not a warm climate at all.
This is a lace web, or lace weaver spider. There are a few species that are relatively common: Amaurobius ferox, Amaurobius fenestralis & Amaurobius similis...the latter being a very likely candidate for your spider.
The brown lace web spiders are the most common spiders I see in my own home, they are capable of delivering a bite, but I have never been bitten by one myself. Bites seem most likely if the spider is caught up in bedding or clothing. I do tend to tip any that I find 'on the loose' outside, but there are undoubtedly many around the home.
However, this doesn't automatically mean that an Amaurobius spider was responsible for your son's bite, there are a few spiders capable of delivering a bite & some can be found as far North as Sweden & Norway. Spider bites are still very rare.
As well as the spider's venom (usually no long lasting effects - a couple days of swelling & soreness?), there is always the possibility of the (or any) bite becoming infected.