I think children start forming their own opinions as soon as they begin to speak. Even the simplest expressions, like saying 'yes' or 'no' to food or a toy, show their preferences and opinions. Their early words are a straightforward reflection of what they like and dislike, indicating the beginning of opinion formation.

When children start expressing their likes and dislikes, they begin to show their personal opinions. This is when they realize they have a say in the family, and they can either agree or disagree with what's happening. For example, if the family plans to eat out, a young child might just say they don't want to go and refuse to follow the plan. This is the child expressing their preference for doing something else, showing their opinion. But whether the family listens to the child's opinion is a different matter.

Children start showing their own opinions when they begin to display clear preferences. This can be seen in their choices of play activities, the friends they make, and what interests them. For instance, preferring certain colors or stories shows they are forming opinions. It's these choices that give us a glimpse into their developing personalities and likes.