At what age should we correct our toddler if s/he is still bulol (stutters)?

I think speech development starts as soon as your child starts to mimic sounds and babbles. And with this, he/she is slowly adapting and observing how the people around him/her acts and speaks. I've read from some articles before that toddler stage is a point where children can easily adapt and follow what they see and hear around them. And with this, it means that the way you interact and converse with your child play great role in his/her speech development. I've seen some parents, even my own relatives, talking the way babies do (for entertainment, yes) but it somehow affects the child if he/she keeps on hearing people speaking that way.