If development is not possible according to the ages of children's may be itself may have a malfunction, or it could be that the trainer can not lack of knowledge and lack of care in child care.
If the development does not meet the age. Maybe it's the children themselves who may have a disorder or a mentor can not be a lack of competence and lack of attention to the care of children.
If the development according to age. May be that of the child may have irregular or may be a nanny that cannot lack knowledge, ability and the lack of attention to child care.