Does anyone - especially those of you in fields like psychology, social work, and the like - have any handy references for data that could help us understand the 5-y/o's mind? Examples - i have wondered about how reliably he could perceive and recall time, what lies a child might tell, concerns about or protocols for interviewing may be unique to children around this stage in development, etc. It has been six or seven years since I took developmental psyc, and I haven't kept up on this kind of research since I went into neuro.
As a psychologist, I can say that it varies from child to child. In my personal and professional experience, a child can tell a lie and stick to it - if it is coming from within the child. However, a child who is told to tell a lie and go along with a story usually can't do it for very long at that age. They may be able to keep repeating what they were told - but not be able to embellish any other details.
For example, if a child were told to lie in this case, and then were asked during questioning, "What were you and Breeann talking about while riding?" or "Did you ride side by side, or were you racing?", a 5-yr-old wouldn't have the reasoning ability to keep embellishing if they were told to repeat a certain story line -- riding bikes, went inside to get a drink, came out, and Breeann was gone. An older child may be able to continue and add to what they were told to say, but not a younger child.
I don't have research to back this up - it's just my own experience/observations. It's fairly easy to catch a young child in a lie, if questions are asked that are open-ended and address things that didn't happen.
Another observation: depending on how old the 5-yr-old is (just turned 5 or almost 6), then a 5-yr-old may not even get concerned if s/he goes back out and can't find their sibling. They may just keep riding and go play with something else, then when asked by an adult where so-and-so is later, just shrug and say they don't know. They don't (usually) have the ability to see the big picture/danger of a child being missing and will assume the other child is playing elsewhere, etc.
Hope this helps...