What do we call parents who lose their child? [duplicate]

I don't know of a specific word for this situation, but bereaved parents fits. To bereave means to suffer a profound loss, especially through the death of a loved one. Associating the word with "parent" will indicate the loss of a child.

If it is an only child we can use the word shidu (or shidu parents) which has been recently introduced into English from Chinese.

Wikipedia explains:

Shidu (失独) is a phenomenon denoting the loss of a parent's only child. The parents who have lost their only child are known as shidu fumu in China.

This might be a bit more specific than what you're looking for but can't hurt to consider.