Toddler wants to breastfeed?

K.A.S • Boy mom x3 Girl mom x1

My youngest son was only breastfed for the first 11 days of his life before my supply dropped due to a traumatic event and I had to stop. His little sister on his dads side is only 7 months younger than him however and she was breastfed but is a year old now and rarely nurses. My son is 19 months old and I'm pregnant with number 3 and I definitely think my colostrum is starting to come in. Well the past week or so almost any time my son is sitting with me or laying with me he pulls my shirt down and tries to put his mouth on my nipple to start nursing. I gently move his head away and tell him no and explain that he's a big boy and that's how babies eat. It actually kind of breaks my heart as I had wanted to breastfeed both of my sons until age 2 and I had to stop with both of them. This morning as I was putting him in the highchair to eat he was persistently pointing to my breast and putting his hand into my shirt and I just did the same thing, explained to him that that's how babies eat and hes a big boy and I was getting his breakfast and milk now. Hes still eating and drinking like normal so I'm not worried, just curious if this has happened with anyone else child or if any one knows why this might be happening? I know kids can sense pregnancy and become clingier and regress a bit but like I said, he hasn't been breastfed since he was 11 days old so that wasnt a norm for him. Maybe he can sense my colostrum coming in and it's still an innate instinct for him at such a young age? My oldest was only a few months older when I was pregnant with him and he never did anything like this.