My 4 year old is still in diapers what should I do?

Toilet Training. Have set times to sit on toilet: first waking up, after breakfast, before and after lunch, mid-afternoon before nap, after nap, before and after supper, before bath and bedtime. Take to store and have child pick out favorite underwear, then remind child that the underwear do not like to get wet or dirty, and keep the underwear happy. Read the different children's books that discuss potty training.