This is probably one of the best things I did with my kids last Christmas and it's easy and free!
Santa's sleigh will be flying over the UK on Christmas Eve - visible in many places but I think sadly not Scotland. It flies over London at about 5.21/5.22pm, and there's an online tracker so you can see when it will be near you if you aren't London-based.
Last year, it took only a couple of minutes to fly over so we were lucky to be looking for it at the right time. It was a bright, strong light - and very clearly different to the usual planes, satellites, stars, etc. My DS was amazed and I have to say I though it was pretty wonderful too. Am looking forward to my DD being able to take part this year, now she's old enough to understand it.
Google 'International Space Station' for more details.