The sound of a child crying can be very distressing for a couple of reasons. Firstly, the mum might worry about what is the matter, especially when young babies are unable to communicate why they are crying. Secondly, it can be a distraction to get anything done due to the noise which can lead to subsequent stress.
The first thing you could do is to seek medical advice. Go to your doctor and check that there is nothing physically wrong with the child, especially because sleeping for only 4 hours in a day would certainly be quite unusual for a child of this age. The doctor will be able to determine this by running a few simple checks to ensure that the child is ok from a medical perspective and that their crying is not a result of any physical ailment.
If the doctor says that they are in good physical health, then it could be simply a result of the child’s age. At the age of 18 months, children do cry a lot. One of the primary reasons children cry is to get attention, and at the age of 18 months, their language skills are far from fully developed. Therefore, they will inevitably have a difficult time in communicating their needs. As you can probably understand, this can be very frustrating when you need or want something but are unable to communicate this in any way.
In order to minimise the crying, the first thing is to ensure their basic needs have been met; that they are not hungry, that their nappy is clean and dry, that they don’t feel too hot or cold..etc. Ensure that they have an activity to keep themselves busy and that they are not crying for something else. It may also just simply be a desire for some love. Children of this age love to be close to people. At this age, as they become more independent, they spend less time in the arms of their loved ones as they run around and play. But there may be moments where they suddenly miss this and just want a cuddle to get a sense of love and security.
As the child gets older, they will be able to communicate their needs and let you know exactly why they are crying and, therefore, will spend a lot less time crying.
May Allah (swt) grant you the patience to bear the constant crying. May He (swt) make this child the coolness of your eyes and make things easy for the child and the family.