I've posted with this name on a similar thread, having experienced the SS side of things in a case very similar to this.
For a start, these are little children we are talking about. They are not "licking cock" or "performing blowjobs", as some helpful
posters have suggested. 4 and 5 yo's generally do not have any sexual awareness at all. Their behaviour is led by discovering their own, and others bodies. The similarities, the differences.
Someone also pointed out that the average 4/5 yo girl wouldn't do anything like this. Yes, you're right, but there are extremes in normality. My next door neighbours little girls would probably do something like this (as would my ds) and they certainly aren't from an abused background.
The case I was involved with (very close family) involved 2 little boys. They were reported to SS. The sw was fresh out of college, had no experience of children at all, and immediately decided that this was clearly a case of abuse, as no normal child would ever lick a willy without having seen this regularly, or having being forced to do this by someone else.
The little boys involved were normal boys, extreme, yes, but normal, but went through months of counselling, having their family lives monitored, and, in one case, being treated completely differently by their parents, as they felt their son was some kind of sexual predator.
After 3 months, the original SW was unable to keep her appointment, and an older lady came in her place, she was so appalled that it had been reported to ss in the first place, went to her seniors, and within a week the whole sorry thing was over.
In her words, one incident does not make a case. Also in her words, at that age, licking willies, whilst not everyday, is something that is done by some children, and certainly does not mean that they have been abused. She felt it should be considered as harmless as little boys and girls comparing their bits, only some children take it a little bit further. Obviously it's not something to be encouraged, and the dc in question need a word from their parents about appropriate behaviour, but it is normal.
One of the boys used to be really sparky, outgoing and a real livewire is now a shadow of his former self. Doesn't want to go to friends houses, doesn't really want to play with anyone unless an adult has told him it's OK.
I hate threads like this, because the majority immediately cry "abuse" without knowing any back story at all, and without knowing the children at all.
At least some have been sensible about this.