diff --git a/public/src/client/category.js b/public/src/client/category.js
index 3aff45420e..b14a80d0c9 100644
--- a/public/src/client/category.js
+++ b/public/src/client/category.js
@@ -89,28 +89,22 @@ define('forum/category', [
 	}
 
 	function handleLoadMoreSubcategories() {
-		$('[component="category/load-more-subcategories"]').on('click', function () {
+		$('[component="category/load-more-subcategories"]').on('click', async function () {
 			const btn = $(this);
-			socket.emit('categories.loadMoreSubCategories', {
-				cid: ajaxify.data.cid,
-				start: ajaxify.data.nextSubCategoryStart,
-			}, function (err, data) {
-				if (err) {
-					return alerts.error(err);
-				}
-				btn.toggleClass('hidden', !data.length || data.length < ajaxify.data.subCategoriesPerPage);
-				if (!data.length) {
-					return;
-				}
-				app.parseAndTranslate('category', 'children', { children: data }, function (html) {
-					html.find('.timeago').timeago();
-					$('[component="category/subcategory/container"]').append(html);
-					ajaxify.data.nextSubCategoryStart += ajaxify.data.subCategoriesPerPage;
-					ajaxify.data.subCategoriesLeft -= data.length;
-					btn.toggleClass('hidden', ajaxify.data.subCategoriesLeft <= 0)
-						.translateText('[[category:x-more-categories, ' + ajaxify.data.subCategoriesLeft + ']]');
-				});
+			const { categories: data } = await api.get(`/categories/${ajaxify.data.cid}/children?start=${ajaxify.data.nextSubCategoryStart}`);
+			btn.toggleClass('hidden', !data.length || data.length < ajaxify.data.subCategoriesPerPage);
+			if (!data.length) {
+				return;
+			}
+			app.parseAndTranslate('category', 'children', { children: data }, function (html) {
+				html.find('.timeago').timeago();
+				$('[component="category/subcategory/container"]').append(html);
+				ajaxify.data.nextSubCategoryStart += ajaxify.data.subCategoriesPerPage;
+				ajaxify.data.subCategoriesLeft -= data.length;
+				btn.toggleClass('hidden', ajaxify.data.subCategoriesLeft <= 0)
+					.translateText('[[category:x-more-categories, ' + ajaxify.data.subCategoriesLeft + ']]');
 			});
+
 			return false;
 		});
 	}
diff --git a/src/api/categories.js b/src/api/categories.js
index 442131b4fd..7cb7a17f69 100644
--- a/src/api/categories.js
+++ b/src/api/categories.js
@@ -85,6 +85,27 @@ categoriesAPI.getTopicCount = async (caller, { cid }) => {
 
 categoriesAPI.getPosts = async (caller, { cid }) => await categories.getRecentReplies(cid, caller.uid, 0, 4);
 
+categoriesAPI.getChildren = async (caller, { cid, start }) => {
+	if (!start || start < 0) {
+		start = 0;
+	}
+	start = parseInt(start, 10);
+
+	const allowed = await privileges.categories.can('read', cid, caller.uid);
+	if (!allowed) {
+		throw new Error('[[error:no-privileges]]');
+	}
+
+	const category = await categories.getCategoryData(cid);
+	await categories.getChildrenTree(category, caller.uid);
+	const allCategories = [];
+	categories.flattenCategories(allCategories, category.children);
+	await categories.getRecentTopicReplies(allCategories, caller.uid);
+
+	const payload = category.children.slice(start, start + category.subCategoriesPerPage);
+	return { categories: payload };
+};
+
 categoriesAPI.setWatchState = async (caller, { cid, state, uid }) => {
 	let targetUid = caller.uid;
 	const cids = Array.isArray(cid) ? cid.map(cid => parseInt(cid, 10)) : [parseInt(cid, 10)];
diff --git a/src/controllers/write/categories.js b/src/controllers/write/categories.js
index e987b433ce..e068f06305 100644
--- a/src/controllers/write/categories.js
+++ b/src/controllers/write/categories.js
@@ -45,6 +45,12 @@ Categories.getPosts = async (req, res) => {
 	helpers.formatApiResponse(200, res, posts);
 };
 
+Categories.getChildren = async (req, res) => {
+	const { cid } = req.params;
+	const { start } = req.query;
+	helpers.formatApiResponse(200, res, await api.categories.getChildren(req, { cid, start }));
+};
+
 Categories.setWatchState = async (req, res) => {
 	const { cid } = req.params;
 	let { uid, state } = req.body;
diff --git a/src/routes/write/categories.js b/src/routes/write/categories.js
index f1e2f39504..9121ee9a7f 100644
--- a/src/routes/write/categories.js
+++ b/src/routes/write/categories.js
@@ -16,8 +16,9 @@ module.exports = function () {
 	setupApiRoute(router, 'put', '/:cid', [...middlewares], controllers.write.categories.update);
 	setupApiRoute(router, 'delete', '/:cid', [...middlewares], controllers.write.categories.delete);
 
-	setupApiRoute(router, 'get', '/:cid/count', [...middlewares], controllers.write.categories.getTopicCount);
-	setupApiRoute(router, 'get', '/:cid/posts', [...middlewares], controllers.write.categories.getPosts);
+	setupApiRoute(router, 'get', '/:cid/count', [...middlewares, middleware.assert.category], controllers.write.categories.getTopicCount);
+	setupApiRoute(router, 'get', '/:cid/posts', [...middlewares, middleware.assert.category], controllers.write.categories.getPosts);
+	setupApiRoute(router, 'get', '/:cid/children', [...middlewares, middleware.assert.category], controllers.write.categories.getChildren);
 
 	setupApiRoute(router, 'put', '/:cid/watch', [...middlewares, middleware.assert.category], controllers.write.categories.setWatchState);
 	setupApiRoute(router, 'delete', '/:cid/watch', [...middlewares, middleware.assert.category], controllers.write.categories.setWatchState);
diff --git a/src/socket.io/categories.js b/src/socket.io/categories.js
index e2b647f71a..a62d55edfe 100644
--- a/src/socket.io/categories.js
+++ b/src/socket.io/categories.js
@@ -167,20 +167,14 @@ SocketCategories.isModerator = async function (socket, cid) {
 };
 
 SocketCategories.loadMoreSubCategories = async function (socket, data) {
+	sockets.warnDeprecated(socket, `GET /api/v3/categories/:cid/children`);
+
 	if (!data || !data.cid || !(parseInt(data.start, 10) >= 0)) {
 		throw new Error('[[error:invalid-data]]');
 	}
-	const allowed = await privileges.categories.can('read', data.cid, socket.uid);
-	if (!allowed) {
-		throw new Error('[[error:no-privileges]]');
-	}
-	const category = await categories.getCategoryData(data.cid);
-	await categories.getChildrenTree(category, socket.uid);
-	const allCategories = [];
-	categories.flattenCategories(allCategories, category.children);
-	await categories.getRecentTopicReplies(allCategories, socket.uid);
-	const start = parseInt(data.start, 10);
-	return category.children.slice(start, start + category.subCategoriesPerPage);
+
+	const { categories: children } = await api.categories.getChildren(socket, data);
+	return children;
 };
 
 require('../promisify')(SocketCategories);