Because I haven't got a clue 
We took baby (3.5 months) for a picnic at the beach near a local lake today. He slept for most of the time. When he woke up I took him down to the sand so he could feel it on his feet. He loved it and was wriggling his toes into it like mad. I noticed some people nearby watching him which I can understand as he is completely gorgeous
.
Then I took him to the water's edge so he could feel it lapping against his feet. Again he was very happy and started shouting at the water in excitement. In total we spent about 5 minutes on the beach. It was about 3.30 and we were under the shade of trees the whole time.
When I turned round to take him back to where we were sitting the people who'd been watching were doing the whole head-shaking/tutting/catsbum thing. What did I do wrong?