Is it normal to be sad about baby growing up?

My son is 20 weeks and I adore him to pieces. He's just changing so quickly and I can't believe how much love I can have for him. 
Is it normal to feel sad when look at his newborn pictures and how much he's changing already? I love him at this stage too but miss him as a brand newborn. 
I find it sad clearing out his wardrobe for his smaller sizes.