You are never being unreasonable to ask a question about more or less anything at all on the fountain of all knowledge that is Mumsnet. Mumsnet usually has an answer for everything, it is an amazing resource and the archive is gargantuan. So when you say "Am I being unreasonable to ask about ..." the answer is always going to be Yanbu, feel free to ask.
The AIBU topic is for those times when something has happened, or something is happening, or something is about to happen that you have an opinion on and you're not sure if your opinion is reasonable or not. It has a sort of check yourself function - you are gathering opinions and trying to work out if you are being unreasonable.
It isn't a place to ask "what are you reading?" or "how big was your second baby compared to your first?" or "can I ask for advice on [insert topic here]. You can ask those questions in Chat or the relevant topic (Adult Fiction, for example).
AIBU is not the only place on Mumsnet!
It makes the site look a bit silly to outsiders, imo. Also, AIBU for some reason has a reputation where it's alright to post with no holds barred. So perfectly reasonable conversations and topics can become a right old bunfight just because people have become used to dropping in their fuck witted so-called "straight talking" points and excusing them with "well this is AIBU after all".
A quick glance at the AIBU list of conversations just now shows at least 10% of them, maybe more, don't belong in the topic. There is an entire topic on low carbing, for example, with hundreds of threads in there.
AIBU to think the site would be massively improved if people put just a little more thought into what they are actually asking and where they are asking it?