Am I over reacting?

Alannah • Wife and mother of 2 boys 10/02/13 and 03/09/19 and 1 princess 05/17/21

I just found out I'm pregnant with my 3rd and final baby. And almost a year ago I was diagnosed with an autoimmune disease (graves disease). Well I haven't told my children. My oldest is 6 and my youngest is 18 months. So I posted in a group I'm in for my graves disease that I was pregnant and wanted to announce to my kids and family on my 6yo birthday on Oct 2nd.. and someone responds "is that fair to your oldest". Am I wrong in taking offense to this. She doesn't know my life or kids... Is she wrong to assume my son would be upset. I mean my son asks my hubby and I Everytime we go into our room if we're gonna make a baby. It irritates me that she assumes it would be unfair of my child to announce my pregnancy at his party which is just my parents, grandparents and my best friend..