Advice on holding a Santa Special family event at the Kent & East Sussex Railway

I work at the Kent & East Sussex Railway where we have held a Quiet Day over the past few years specifically for people on the autism spectrum. The site is intentionally kept a lot quieter on those days, but with children still having the opportunity to enjoy a festive experience. This has been incredibly successful and is something I would like to be able to offer again this year, however I am struggling to find a suitable date and time when the town isn't also busy with Christmas events. My question where I am hoping for advice from the experts please is, if I were to offer a Santa Special train early evening on Friday 17th December, the last day of term, would you consider this to be a suitable time to bring children to the event or would this be too overwhelming for them having the final day of school and then an outing to meet Santa on the same day?  I appreciate this isn't a one size fits all as everyone is different but it would be great to get an idea of whether this would be viable.

Thank you in advance for your help.