This morning, at about 11am, I went outside and found white fuzzy patches growing on the exposed soil of my lawn in a shady spot (in north-west England). It does not appear to be on the grass itself. See attached images. On closer inspection, it was also present on the soil under the grass in the non-shady non-exposed spots. I've searched the internet and this stackexchange, and have come across several white growths on soil, but nothing looks quite like this. I'm assuming it is some sort of mould or fungal growth. I'd like to know what it is, whether it is harmful, either to the grass or to a child, and whether it will go away on its own or if there is something I can do to treat it.
Some background: I recently thoroughly dethatched the lawn with a manual rolling scarifier as it had a significant thatch (and probably moss) problem. I applied EVERGREEN NO MOSS NO RAKE lawn feed at the recommended rate with a hand-held spreader, as well as lawn seed (various varieties left over in old boxes, maybe up to a year old), and then treaded and watered it in. I then watered with a sprinkler for about 20 minutes a couple of times a day. This was exactly one week ago. The grass and soil got quite wet, and I'm thinking it might not have needed the extra water, but I was worried about the soil drying out (it had been very dry prior to the overseeding) and causing problems with the new seedlings.
Thanks for any advice!