For the second time in one evening, I find myself in the unusual position of agreeing with Norman ;-)
The National Rail Museum is great fun for all ages:
http://www.nrm.org.uk/home/home.asp
The Model Railway (next to the station) is also quite popular with children:
http://www.britainexpress.com/cities/york/mode lrailway.htm
As well as looking at trains, why not travel on one? There's an hourly direct service to Halifax. (Journey time about 1� hours. Adult return fare �10.40). Why Halifax? Because, right next to the station, you'll find Yorkshire's star attraction for youngsters, Eureka!
http://www.eureka.org.uk
Where did you get the information which suggests that Jorvik closes at the end of October? I suspect that it may have been from the York tourism site:
http://www.visityork.org
That site certainly refers to the 'season' ending at the end of this month but it doesn't seem to tie in with what the Jorvik website says:
http://www.jorvik.co.uk/
There's no reference to a season' but there is advice to the effect that 'times may vary over Christmas'. That seems to suggest that Jorvik is open all year round. For definitive information, phone the centre on 01904 543400.
Chris