This is a suitable induction method for children.
Draw a smiley face on the thumb nail and ask the subject to hold the arm out at arm's length and keep the eyes focused on the smiley face.
Suggest "As you focus on the thumbnail notice how the arm is becoming heavier and heavier. Just so heavy now that it begins to feel like its being weighed down.
And as the arm gets heavier notice how the eyelids also become heavier and heavier. Heavier and heavier. Those eyes feeling sleepy, so sleepy and so heavy, so comfortable, and so relaxed." Keep repeating suggestions of heaviness and sleepiness until you get eye closure, but don't worry if you just get a 'glazed' look in the eyes as this is an indicator that the child has drifted into a comfortable state of hypnosis.
Many children don't actually close their eyes during hypnosis but that faraway look is a giveaway. I once knew a young child who nearly always slept with his eyes wide open. Children can also get fidgety as they are not used to sitting still for too long, so try not to prolong the hypnosis unnecessarily.