My 18m toddler has been scratching her diaper area ie around the waist and groin area. I am not sure if it is due to the humid weather recently. I have tried to loose the diaper and applied moisturiser/desitin but it doesn't seem to be getting better. What else I can do to ease her itching?

High chance it's due to the weather. You can try him on cloth diaper instead. You will have no choice to change the cloth diaper once wet, therefore, it will be less humidity involved. If you do not have a cloth diapers, try to change the diapers every 2 hrs. Try not to let it b wet for too long elae it may later lead to unnecessary infection.