what to do with a child who

really doesnt seem to grasp simple concepts like taking off yesterdays underwear before putting on todays? He HAD been dressing himself no problem but after my being gone a long time he has reverted back to crying and wanting me to do it. it now takes twice as long as it used to for him to dress himself. and he has no concept of take off the old before putting on the new. since he wears afos and has trouble standing he has a hard time getting them off again. Then again maybe they didnt change undders at the orphanage every day. I know the girls get a bath x1 a week. so maybe underwear change/clothes change is only1x aweek.