Thank you for asking this! This has been bugging me recently, and I think it needs to be addressed.
As Torben mentions, not all questions require research and citations, simply because some questions are about subjects for which there is no research. However, I disagree that it should be up to the asker to specify if they want research and citations when available (although a reminder from the asker can't hurt).
I believe it should be fairly self-evident, based upon the question, whether research and citations should be included. Questions about risks ("is x safe?"), health, developmental milestones, or anything for which research is likely to be performed (e.g. "what is the impact of television on young children?") should absolutely include citations and/or references in every answer.
For other questions, such as practical advice on behavior, routines, or tips and tricks to help reach known milestones (e.g. "how do I get my kid to sleep?"), research and citations aren't likely to be possible. However, answers should still reference personal experiences, and not merely speculation.
Per our faq: "Please note that opinions shared here should be backed up either with a reference, or experiences that happened to you personally."