How can you help your child come out of this state?
Good parenting no doubt helps foster self confidence in the child. Children whose parents have themselves suffered depression have high probabilities of early depressive symptoms.
Watch out for the signs of depression as a responsible parent. Help developing coping strategies in your child. Give a patient ear to your child’s talk and do not shirk them as unimportant. Its these talks that not only strengthen your bond with the child but also give your child a sense of self and a source of venting out.
Reinforce positive feelings in your child. Foster the sense of being wanted and loved.
Take your child to a professional if you are not in a situation to handle him. It is never too late to learn.

Can an occupational therapist or pediatric rehabilitation therapist help your child?
Yes. A rehabilitation professional with adequate knowledge of child psychology can prove of immense benefit to your child. Your therapist will be able to evaluate and help you understand your child better. A psychiatric consultation may also be necessary.
Play therapy is one of the apt methods to not only evaluate but also to rehabilitate children with low self esteem, decreased interest in activities.