gsr600 - I caught one of my three year olds climbing out of the washing machine earlier (they are only allowed in the kitchen when I am in there (there is a stair gate in the door way to keep them out) but he still managed it).
Some machines will lock the door if there is water in them, so starting a cycle and then turning the machine off after it's let some water in would do it on a few...
Though that would be a pain as you'd have to run a drain part of the cycle before you use it (and I suspect the pressure system would leak a little over time and it would eventually let the door be opened anyhow.)
Hi chuck - I could try that until I get the safety gizmo thing! (I was gobsmacked when I saw him climbing out - he's supposed to be the good twin, god help me when the evil twin cottons on.)
i'd be carful when leaving water in it, mine unlocks after not being used for just 15 mins. Could you not just put them on the "naughty step" when they do it? i'm sure that would get them to stop.