AIBU to have inwardly smiled at this? Despite feeling a bit bad that it was my DS's fault...
Yesterday in the library my DS, 18 months, walked up to a crawling baby c. 12 months and tried to hit her. Not hard at all and certainly not maliciously; he missed her, and in any case it was so gentle the other baby didn't even look up (!). But obviously hitting is wrong, I never allow it, and I took him to one side and gave him a little time out.
The other baby's mother, however, looked absolutely horrified, grabbed her child away, and said "I've never seen anything like that before in my life"!
I did think... she'll learn!