Taylor wrote it from the perspective of the little boy's mum, who wrote a blog covering her experience looking after her son and include the lyrics 'I love you to the moon and back, you were my best four years.'
It's a really touching song, and Taylor debuted it at the Stand Up To Cancer Telethon this week. She couldn't hold in her emotional connection to the song, and burst into tears when the performance was over.
Check out both the live and recorded versions of the track here.