Even more so when they don't have children of their own. So today DH had the "my children would/would not do this/that", "I would do that with my children" etc - these are non-existent children as they decided not to have any anyway!
SIL - My friends children don't make a mess and spoon fed is better
DH - PFB is BIL and exploring her food and eats everything and clearly spoon feeding is going to be tidier
SIL - My children would not watch tv (not sure what this comment was actually based on)
DH - PFB doesn't watch TV, she reads lots of books and (according to nursery) her speak to really good for her age.
I did try to get her to watch a bit of Crufts as she loves dogs but she wasn't even interested in that 
SIL - My Mother stayed at home with me for the first 3 years, Mums should be at home with their children
DH - Well it works for us and pfb is very happy
Thankfully DH also realises it is acceptable for us both to work and thankfully, as I was at work today he had to put up with all of the above on his own and made his feelings clear.
Oh and them wanting to use pfb as a Guinea Pig and have their dog in the same room (even though it was growling when DH turned up at the door)
Good job they live in another country most of the time 