Thank you for posting your question.
The number of hours of sleep that can be considered adequate for any child is usually individualized. It depends on the pattern that has been formed from the beginning, the diet that the child consumes, the level of activity the child has , the routine of other members of the family, the sleep conditions provided to the child in the house etc. Although sleep is also likely to be affected in any disease process going on in the body, if decreased sleep is a routine affair for the child then it is unlikely that it would be due to any illness.
The process of ensuring good sleep for the child would be long, requiring continous efforts and patience. Certain tips that could be used include increasing the level of activity in the child, avoiding day time sleep as much as possible, giving a glass of milk before bed, giving a warm bath before bed, making sure other family members are asleep and lights switched off in order to provide an ambience to the child etc.
Having said so, one cause that is often overlooked and causes sleep disturbances in a lot of children is
obstructive sleep apnea. This occurs due to obstruction in any part of the upper airway due to either a deviated nasal septum/ tonsillar enlargement/allergy/cold/obesity etc. It usually manifests in the form of
snoring and disturbed sleep at night and is considered if it causes day time irritation/
lethargy or other system involvement. If it is suspected consulting a doctor would be advisable.
Apart from this, the habit of eating unedible substances also known as
pica could be due to deficiency or iron or calcium which may be corrected be giving supplements.