This article is about experts finding that babies start lying as young as 6 months old. From the article:
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.
By the age of two, toddlers could use far more devious techniques, such as bluffing when threatened with a punishment.
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.