Talk to Moose a few times until he asks you to give Nightlight a pink tulip. Give the tulip to Nightlight and talk to Moose again. Go back to Nightlight and answer "no" to her question. Go back to Moose and talk to him. Wait until a new moon and go inside the tent, where Grasswhistle and Moose will be. Talk to them, them go back to Nightlight and talk to her again.