Starting at six months old, apparently:
Following studies of more than 50 children and interviews with parents, Dr Vasudevi Reddy, of the University of Portsmouth's psychology department, says she has identified seven categories of deception used between six months and three-years-old.
Infants quickly learnt that using tactics such as fake crying and pretend laughing could win them attention. By eight months, more difficult deceptions became apparent, such as concealing forbidden activities or trying to distract parents' attention.
Dr Reddy said: "Fake crying is one of the earliest forms of deception to emerge, and infants use it to get attention even though nothing is wrong. You can tell, as they will then pause while they wait to hear if their mother is responding, before crying again.
I still do this with the wife. Works like a charm.