Your child has to be able to master several skills in order to become independent in going to the toilet. Once they have gained control over their bladder and bowel they need to learn how to clean themselves. This involves being able to reach behind themselves, being able to turn their hand, and knowing where to wipe.
The following ideas are to help your child master these skills:
Retrieve a scarf or handkerchief tucked into the back of the waistband, with either hand. Progress to learning to tuck it back in again, partially at first then fully. If necessary use a full length mirror to help.