Does anyone use essential oils and a diffuser, I’m trying to get rid of my 16 month olds allergies and cough but have…

Does anyone use essential oils and a diffuser, I’m trying to get rid of my 16 month olds allergies and cough but have zero clue where to start. I got a diffuser that hold 100ml of water and put two drops of lemon two drops of lavender and two drops of tee tree oil.