To calculate the dose of Benadryl for children, you can give 1 to 1.25mg of the product per kg of your child's weight every 4 to 6 hours, for a maximum of 4 times a day. For example, for a child weighing 12kg, this would be approximately 12 mg four times a day. The solution for children is usually concentrated at 6.25mg/5ml, so this would equate to about 9ml. For a child weighing 23kg, the dose would be around 18ml. It's important to reduce the dose or frequency if it causes excessive drowsiness.