Young children do not know the difference between weekdays and weekends. When my kids were young, they would come to my bed every morning asking whether I had to go to work this day.
To give me some peace in the weekends I made a clock that would turn in seven days. The dial has a red coloured figure on it in the shape of a "W" (= weekend!). It is exactly 2/7 th of the dial.
When the indicator is in the red area, it is weekend, SO BE QUIET AND STAY IN YOUR ROOM!
PS The clock is from an old chart_recorder, but you could hack the mechanism of an ordinary clock.
The knob on this model (second picture) allows you to set it montly, weekly, hourly...And yes, this one is explosion proof!
The dial is simply attached to the clock with double-sided tape.