I appreciate there are a plethora of virtual runs, not least in December but here are 3 that may resonate with your runners:
 
Rudolphrun
Charity: Little Rainbows Autism Group (Registered Charity 1121130)
5k
December 1st-8th
£10 – Medal for all
https://racebest.com/races/fs792
 
Boxing Day Turkey Trot
Charities: Cathedral Archer Project (1064818), Bluebell Wood Children's Hospice (1076958), Alzheimer's Society UK (296645) and Blind Dog Rescue UK (1148828)
5k or 10k
December 26th
£15 – Medal and personalised t-shirt for all
https://racebest.com/races/sa52x
 
Virtual Santa Dash
Charities: Cathedral Archer Project (1064818), Bluebell Wood Children's Hospice (1076958), Alzheimer's Society UK (296645) and Blind Dog Rescue UK (1148828)
5k or 10k
Any time in December
£15 – Medal and personalised t-shirt for all
https://racebest.com/races/w8q4f
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Nemesis Infinity is a 6 hour endurance challenge, priced at £35.
 
It is set on the stunningly hilly part of the  Cleveland Way running a loop just over a 1.3miles in length with a few inclines added for good measure.
 
This event has a great bunch of friendly marshals and you get fed afterwards.
 
This event supports the work of Scarborough and Ryedale Mountain Rescue team.
 
Because of the time of year you will be expected to have winter kit including a cup, waterproof jacket with taped seams, hat, gloves, head torch, reflective items e.g. vest or snap bands or glow sticks, waterproof trousers are advisable in your kit. In the previous 4 years of the event we have had EVERY weather you can imagine!