I have a Facebook friend who constantly calls her child her Rainbow Baby. Every time she posts a picture of him, she said 'my rainbow baby' 'my little rainbow' etc etc. The child is a around 2-3.
I get it, having a MC is devastating and having a baby after that will feel extra special. Maybe the term rainbow baby is appropriate during pregnancy but I find calling a toddler a rainbow baby a bit ... strange. I would hate it if that was my identity - I would want to be known as an individual IYSWIM.