I don't think these are funny either, and I agree with all of you who find them inappropriate.
However, as far as advertising goes, as far back as I can remember there were babies and children photographed for advertisements. As a small child I would have loved to be one of them!
At least that is what I thought at the time - the reality of having to stand still and be good for so long would probably have sicken me off it very quickly.
Fortunately, my parents would never have consider allowing me to become a photo model as a child. But some parents did, presumably in an attempt to provide for their children on a very small income. There are still parents trying to do that.
As to all the supposedly funny - in reality crude sentences on tee-shirts and baby clothes: our generation is appalled, but what do young parents feel? A lot must buy these things, or they would not continue to be sold and worn.
My grandparents disapproved of certain things my parents found funny. Some of our clothes were simply not worn when Grannie and Grandpa came to stay for a couple of days, and my parents modified their language and funny stories out of respect for Daddy's parents' known views.
My point being that we are back to the generation-gap here to a certain extent.
One of the worst t-shirts was worn by teenagers - it stated bluntly "Fuck me!" (remember it?). I wondered at the time whether anyone wearing that shirt could have go the police to take an accusation of rape seriously. I know it wasn't meant as an invitation, but honestly, how could you substantiate it as not being an open invitation to all and sundry?