How to set read write permission on child doctype?

{“exc”:“["Traceback (most recent call last):\n File \"/home/frappe/frappe-bench/apps/frappe/frappe/\", line 67, in application\n response = frappe.api.handle()\n File \"/home/frappe/frappe-bench/apps/frappe/frappe/\", line 111, in handle\n doctype, **frappe.local.form_dict)})\n File \"/home/frappe/frappe-bench/apps/frappe/frappe/\", line 939, in call\n return fn(*args, **newargs)\n File \"/home/frappe/frappe-bench/apps/frappe/frappe/\", line 31, in get_list\n check_parent_permission(parent)\n File \"/home/frappe/frappe-bench/apps/frappe/frappe/\", line 322, in check_parent_permission\n raise frappe.PermissionError\nPermissionError\n"]”}

I am also getting the same error. How to resolve this issue?

Yes. and i dont have fix. For places when i need to access a child object i just find a work around. My solution API does not support child object read. there is way to do it but i dont kno whow.