Oh no choo choo!

HUMM?
Children eh?
Little buggers are quite good at distroying just about anything, in ways
you couldn't eve imagine!

Perhaps the best thing is some form of interlock (So that the blocks will
only go on one way) and to this mould  your interface connector, large
bannana plugs may also be good (But would need to be short and in some form
of schrowd so that they could not stab thier eyes out (Oh the little
darlings). Also the electronics within must be protected so that they can
not be swollowed, or even removed without the aid of a large sledge
hammer!. The plasic used should be of a non toxic type etc. Not simple by
any means

The electronic side is simple, it will be the implementation that is hard!
The train would have been easyer <G>

Dennis