The appropriate dose of Lax a day for a 6-month-old baby can vary between 10% to 40% of a 17g measure, so giving 1/4 of a measure is suitable. It is recommended to mix the powder with water or juice for the best results. Milk or applesauce may not work as well since they are slightly solid. Keep track of how the baby responds to the juice and adjust accordingly. It is important to consult with a healthcare professional for personalized advice.