Answer:
Hi, I don't know if there is any option for this question because you didn't put any, but anyways we can infer that your answer is that Julia learned to suspect from children's stories told by adults because she chats with other kids that already know the truth about these tales.
Step-by-step explanation:
According to these lines, Julia has found out some stories told by her parents; this is due to the conversations children start to have when they socialize. It is very common that, at that age, some children start to suspect what really happens at Christmas, for example; how they receive the presents, how they usually get exactly what they asked for, etc. At this point, some parents decide to tell them the truth and that is how their children, when talking to others at school, sports club, etc tell others that didn't know or suspected anything. The answer is that Julia learned to suspect from the tales told by her parents because she chats with other children that have the same doubts or that already know what happens with Santa or the Stork.