Slapped Cheek or not?

[Bunnygotwhacked]

DD 10 has been fine other than a small sniffle and a cough last night I noticed a small patch of red on one of her cheeks which has now grown to cover most of cheek the other one is looking pinker IYSWIM but is nowhere near as red it isn't itchy. Does this sound like slapped cheek? Would my other two be coming down with it as they have both got quite nasty sniffles at moment?
We haven't had this before so unsure. NHS direct says as it is just a virus it is self care so not an awful lot of use to try wangle an OOH appointment is there?
Is it supposed to be contagious? We are due to have a child to play tomorrow should I cancel do you think?

Slapped cheek is dangerous to pregnant women and is very contagious so yes I'd probably cancel.

When ds had what we think was SC he got a bright bright red face on the Saturday but was otherwise fine. On the Sunday his temp was 39-40 for about 24 hours and the rash spread across his body and looked lacy and mottled. After the temp went e got about 50 ulcers in his mouth but I'm not sure if this wasn't part I something else tbh.