diff --git a/nanostack/thread_diagcop_lib.h b/nanostack/thread_diagcop_lib.h
index 48b8399d53c..cbe721f8be7 100644
--- a/nanostack/thread_diagcop_lib.h
+++ b/nanostack/thread_diagcop_lib.h
@@ -55,7 +55,8 @@
 #define DIAGCOP_TLV_SUPPLY_VOLTAGE                          15  /**< Can not reset*/
 #define DIAGCOP_TLV_CHILD_TABLE                             16  /**< Can not reset*/
 #define DIAGCOP_TLV_CHANNEL_PAGES                           17  /**< Can not reset*/
-#define DIAGCOP_TLV_TYPE_LIST                               18  /**< List type*/
+#define DIAGCOP_TLV_TYPE_LIST                               18  /**< Cannot reset*/
+#define DIAGCOP_TLV_MAX_CHILD_TIMEOUT                       19  /**< Cannot reset*/
 
 /**
  * \brief Write array TLV.
diff --git a/source/6LoWPAN/Thread/thread_diagnostic.c b/source/6LoWPAN/Thread/thread_diagnostic.c
index fdce83ece82..6f74c6075d2 100644
--- a/source/6LoWPAN/Thread/thread_diagnostic.c
+++ b/source/6LoWPAN/Thread/thread_diagnostic.c
@@ -254,6 +254,7 @@ static uint8_t *thread_diagnostic_get_build(protocol_interface_info_entry_t *cur
     uint8_t *ptr;
     int written_address_count = 0;
     uint16_t ipv6_address_count = 0;
+    uint32_t max_child_timeout = 0;
     uint8_t extended_address[8] = {0};
 
     arm_net_interface_address_list_size(cur->id, &ipv6_address_count);
@@ -352,6 +353,12 @@ static uint8_t *thread_diagnostic_get_build(protocol_interface_info_entry_t *cur
             response_ptr = thread_diagcop_tlv_data_write_uint8(response_ptr, DIAGCOP_TLV_CHANNEL_PAGES, 0);
             break;
 
+        case DIAGCOP_TLV_MAX_CHILD_TIMEOUT:
+            if (thread_router_bootstrap_child_max_timeout_get(cur, &max_child_timeout) == 0) {
+                response_ptr = thread_diagcop_tlv_data_write_uint32(response_ptr, DIAGCOP_TLV_MAX_CHILD_TIMEOUT, max_child_timeout);
+            }
+            break;
+
         default:
 
             break;
diff --git a/source/6LoWPAN/Thread/thread_router_bootstrap.c b/source/6LoWPAN/Thread/thread_router_bootstrap.c
index 0a4a2741168..4c061ce934d 100644
--- a/source/6LoWPAN/Thread/thread_router_bootstrap.c
+++ b/source/6LoWPAN/Thread/thread_router_bootstrap.c
@@ -1196,6 +1196,32 @@ static int mle_attach_child_id_response_build(protocol_interface_info_entry_t *c
 
 
 }
+
+int thread_router_bootstrap_child_max_timeout_get(protocol_interface_info_entry_t *cur, uint32_t *max_child_timeout)
+{
+    uint16_t router_address = thread_info(cur)->routerShortAddress;
+    uint32_t max_timeout = 0;
+    if (router_address >= 0xfffe) {
+        router_address = mac_helper_mac16_address_get(cur);
+    }
+    if (router_address & THREAD_CHILD_MASK) {
+        return -1; //I am child
+    }
+    if (router_address >= 0xfffe) {
+        return -1;
+    }
+    mac_neighbor_table_list_t *mac_table_list = &mac_neighbor_info(cur)->neighbour_list;
+
+    ns_list_foreach(mac_neighbor_table_entry_t, cur_entry, mac_table_list) {
+        if (thread_router_addr_from_addr(cur_entry->mac16) == router_address &&
+                !cur_entry->ffd_device && cur_entry->lifetime > max_timeout) {
+            max_timeout = cur_entry->lifetime;
+        }
+    }
+    *max_child_timeout = max_timeout;
+    return 0;
+}
+
 uint16_t thread_router_bootstrap_child_count_get(protocol_interface_info_entry_t *cur)
 {
     uint16_t child_count = 0;
diff --git a/source/6LoWPAN/Thread/thread_router_bootstrap.h b/source/6LoWPAN/Thread/thread_router_bootstrap.h
index 0143ce1e30c..5ab9f3fa087 100644
--- a/source/6LoWPAN/Thread/thread_router_bootstrap.h
+++ b/source/6LoWPAN/Thread/thread_router_bootstrap.h
@@ -52,6 +52,9 @@ int thread_router_bootstrap_mle_advertise(struct protocol_interface_info_entry *
 void thread_router_bootstrap_child_information_clear(protocol_interface_info_entry_t *cur);
 int thread_router_bootstrap_reset_child_info(protocol_interface_info_entry_t *cur, struct mac_neighbor_table_entry *child);
 uint16_t thread_router_bootstrap_child_count_get(protocol_interface_info_entry_t *cur);
+
+// max_child_timeout is longest MLE Timeout a router has registered for all of its active MTD children
+int thread_router_bootstrap_child_max_timeout_get(protocol_interface_info_entry_t *cur, uint32_t *max_child_timeout);
 void thread_router_bootstrap_child_id_handler(struct protocol_interface_info_entry *cur);
 void thread_router_bootstrap_child_id_reject(struct protocol_interface_info_entry *cur);
 void thread_router_bootstrap_router_id_request(struct protocol_interface_info_entry *cur, uint8_t status);
@@ -81,6 +84,7 @@ void thread_router_bootstrap_address_change_notify_send(protocol_interface_info_
 
 #define thread_router_bootstrap_child_information_clear(cur)
 #define thread_router_bootstrap_child_count_get(cur) 0
+#define thread_router_bootstrap_child_max_timeout_get(cur, max_child_timeout) 0
 #define thread_router_bootstrap_child_id_handler(cur)
 #define thread_router_bootstrap_child_id_reject(cur)
 #define thread_router_bootstrap_router_id_request(cur, status)