How do I make sure that the bath and shower water for my children is never too hot?

Water heater temp. Set your water heater at 120degrees maximum and then check the water temp with your own skin each time you bath your child.
Several steps help. If you have accesss the water heater you need to locate a knob where you can set the water temperature. This is usually a dial with hash marks, set for 110 rather than the 130-140 commonly set at installation.Your water may not stay as hot as you are used to but this helps. Testing shower & bathwater with the back of your hand helps, never test with a gloved hand & stay with young children.