When working under the eyes, have your model look upwards - only with the eyes, without moving the head. If you work above the eyes (eyelid), have your model close his/her eyes in a relaxed manner.
Children are inclined to shut their eyes tight. Then you can say: keep your eyes closed as if you are sleeping.
General tip: Water Make-up can be used to add (additional) colour to the hair and eyebrows, provided that the hair is not permed, bleached or dyed. Use a toothbrush to do this. Hair that has been coloured using Water Make-up (Pure) can be washed with shampoo.