‘Weird’ question regarding older children and breastmilk

I have a 6 year old and 4 year old, I’m pregnant with baby #3. I pumped when my kids were little babies and I plan to do the same this time around. When I pumped for my second baby, my oldest was 18months and I gave her breastmilk as well.

I’m wondering if it’s still beneficial to them now at this age if I give them breastmilk? Obviously it’s not going to be ‘socially acceptable’ but that’s something I don’t really care about because they are my children. But if it’s still beneficial to them and their health, I think I’d like to give it to them on occasion.