diff --git a/moto/organizations/models.py b/moto/organizations/models.py
index 609ce3831..2e0d6b40d 100644
--- a/moto/organizations/models.py
+++ b/moto/organizations/models.py
@@ -195,28 +195,6 @@ class OrganizationsBackend(BaseBackend):
             ]
         )
 
-    def list_parents(self, **kwargs):
-        if re.compile(r'[0-9]{12}').match(kwargs['ChildId']):
-            parent_id = [
-                account.parent_id for account in self.accounts
-                if account.id == kwargs['ChildId']
-            ].pop(0)
-        else:
-            parent_id = [
-                ou.parent_id for ou in self.ou
-                if ou.id == kwargs['ChildId']
-            ].pop(0)
-        return dict(
-            Parents=[
-                {
-                    'Id': ou.id,
-                    'Type': ou.type,
-                }
-                for ou in self.ou
-                if ou.id == parent_id
-            ]
-        )
-
     def create_account(self, **kwargs):
         new_account = FakeAccount(self.org, **kwargs)
         self.accounts.append(new_account)
@@ -255,5 +233,43 @@ class OrganizationsBackend(BaseBackend):
         index = self.accounts.index(account)
         self.accounts[index].parent_id = new_parent_id
 
+    def list_parents(self, **kwargs):
+        if re.compile(r'[0-9]{12}').match(kwargs['ChildId']):
+            obj_list = self.accounts
+        else:
+            obj_list = self.ou
+        parent_id = [
+            obj.parent_id for obj in obj_list
+            if obj.id == kwargs['ChildId']
+        ].pop(0)
+        return dict(
+            Parents=[
+                {
+                    'Id': ou.id,
+                    'Type': ou.type,
+                }
+                for ou in self.ou
+                if ou.id == parent_id
+            ]
+        )
+
+    def list_children(self, **kwargs):
+        if kwargs['ChildType'] == 'ACCOUNT':
+            obj_list = self.accounts
+        elif kwargs['ChildType'] == 'ORGANIZATIONAL_UNIT':
+            obj_list = self.ou
+        else:
+            raise ValueError
+        return dict(
+            Children=[
+                {
+                    'Id': obj.id,
+                    'Type': kwargs['ChildType'],
+                }
+                for obj in obj_list
+                if obj.parent_id == kwargs['ParentId']
+            ]
+        )
+
 
 organizations_backend = OrganizationsBackend()
diff --git a/moto/organizations/responses.py b/moto/organizations/responses.py
index 6684ae685..966c3fbf3 100644
--- a/moto/organizations/responses.py
+++ b/moto/organizations/responses.py
@@ -80,3 +80,8 @@ class OrganizationsResponse(BaseResponse):
         return json.dumps(
             self.organizations_backend.move_account(**self.request_params)
         )
+
+    def list_children(self):
+        return json.dumps(
+            self.organizations_backend.list_children(**self.request_params)
+        )
diff --git a/tests/test_organizations/test_organizations_boto3.py b/tests/test_organizations/test_organizations_boto3.py
index 2b692489f..496bcd74d 100644
--- a/tests/test_organizations/test_organizations_boto3.py
+++ b/tests/test_organizations/test_organizations_boto3.py
@@ -341,3 +341,44 @@ def test_list_parents_for_accounts():
     response02['Parents'][0].should.have.key('Id').should.equal(ou01_id)
     response02['Parents'][0].should.have.key('Type').should.equal('ORGANIZATIONAL_UNIT')
     #assert False
+
+
+@mock_organizations
+def test_list_chidlren():
+    client = boto3.client('organizations', region_name='us-east-1')
+    org = client.create_organization(FeatureSet='ALL')['Organization']
+    root_id = client.list_roots()['Roots'][0]['Id']
+    ou01 = client.create_organizational_unit(ParentId=root_id, Name='ou01')
+    ou01_id = ou01['OrganizationalUnit']['Id']
+    ou02 = client.create_organizational_unit(ParentId=ou01_id, Name='ou02')
+    ou02_id = ou02['OrganizationalUnit']['Id']
+    account01_id = client.create_account(
+        AccountName='account01',
+        Email='account01@moto-example.org'
+    )['CreateAccountStatus']['AccountId']
+    account02_id = client.create_account(
+        AccountName='account02',
+        Email='account02@moto-example.org'
+    )['CreateAccountStatus']['AccountId']
+    client.move_account(
+        AccountId=account02_id,
+        SourceParentId=root_id,
+        DestinationParentId=ou01_id,
+    )
+    response01 = client.list_children(ParentId=root_id, ChildType='ACCOUNT')
+    response02 = client.list_children(ParentId=root_id, ChildType='ORGANIZATIONAL_UNIT')
+    response03 = client.list_children(ParentId=ou01_id, ChildType='ACCOUNT')
+    response04 = client.list_children(ParentId=ou01_id, ChildType='ORGANIZATIONAL_UNIT')
+    #print(yaml.dump(response01, default_flow_style=False))
+    #print(yaml.dump(response02, default_flow_style=False))
+    #print(yaml.dump(response03, default_flow_style=False))
+    #print(yaml.dump(response04, default_flow_style=False))
+    response01['Children'][0]['Id'].should.equal(account01_id)
+    response01['Children'][0]['Type'].should.equal('ACCOUNT')
+    response02['Children'][0]['Id'].should.equal(ou01_id)
+    response02['Children'][0]['Type'].should.equal('ORGANIZATIONAL_UNIT')
+    response03['Children'][0]['Id'].should.equal(account02_id)
+    response03['Children'][0]['Type'].should.equal('ACCOUNT')
+    response04['Children'][0]['Id'].should.equal(ou02_id)
+    response04['Children'][0]['Type'].should.equal('ORGANIZATIONAL_UNIT')
+    #assert False