I was just there with my young kids.
Nothing especially not kid friendly unless girls standing around in maid costumes passing out flyers are upsetting. As Thomas said you can avoid any not kid friendly places by not going into them.
When I went to Akihabara I did see some adult comics out in the open in one of the multi level stores I went into. I asked my Japanese friend I was with about this concerned about minors seeing something like this. He stated it was common knowledge somehow that the shop/area of the shop was adult in nature and kids shouldn't be in there. I didn't see anything that would have led me to believe that on the outside so it might be a good idea to be careful.
Maid cafes are certainly not offensive or "adult" - not unless they are actually a girl-bar in disguise and then you would need to be 20 to get in. Bear in mind that most (all) combini have porn magazines on display and hotels usually still have adult channels all across Japan, so identifying Akiba as inappropriate seems a little odd (for locals and visitors). I would not be worried about taking young people there.
Akihabara; the stores on the ground floors are okay for adults and kids, make sure you take lead and eye ball the walls when you start going up stairs or down stairs. They are small signs that are posted informing y adults 18 older or adult stuff. Sadly, this is not in every anime stores you go to outside of Akihabara.
For the maids you see on the street; don't ask to take them pictures they will say no, but you can freely ask.