Essential oils should be diluted properly when using on children topically (do not use essential oils internally unless under the care of a qualified care provider). Only a few essential oils are recommended for babies under 1 years old and a few more after the first year. For children, dilute the essential oil to 1%. For small babies dilute down to .05%. An example of what this means ~
To dilute to 1%, take 1 oz (2 tablespoons) of a carrier oil like sweet almond, apricot kernel, olive oil and then add 5-6 drops total of the essential oil. This is a safe dilution for children.
Learn more on this video about diluting essential oils for children.