Friends and LPN nodes are only used in Bluetooth Mesh.
In Zigbee we have routers (parents) and children nodes. Zigbee routers have its radio always turned on. Children are called Zigbee End Devices (ZED) and can either be Sleepy (design for low power operations) or Non-sleepy (always powered).
In our examples in the SDK you can set the define MAX_CHILDREN in main.c which is use in zb_set_max_child to set the maximum number of connected devices in the project. Default value is 10.
The default maximum value of children nodes for the ZBOSS stack is 32, but we haven't perform any run test using the nRF52840 using this configuration.
