Sechunkmens Messenger Bag Shoulder Bag, messenger bag

Q: I'm wondering if the large would be big enough for my middle school age child, books, binder, folders, lunch box, etc. Thoughts?

I have the small and mine holds everything, including the kitchen sink. My sister got curious one day and went through my bag and found a bottle of pepto bismol, 2 socket wrench sets, 2 wallets including my large brick shaped wallet, my kindle, my cell phone, enough sanitary pads for the women's Olympic team, assorted pens and pencils, notebooks, and every receipt or scrap of paper I've ever picked up for maybe 3 years? It doesn't seem that big at first but it's a magical bag of holding I swear! And it takes a beating which is why I wanted a canvas bag to begin with. I'm not kind to my bags so this has been thrown on floors, in cars, in lockers, in desk drawers, hung on chair backs, and smacked into any surface in my way in the go and it has no tears or marks anywhere. My only complaint really is all that weight hurts your back, but that's my fault not the bags.

Q: Can you tell me or decribe how the side pockets are closed or what get are secured with? I cannot see them clearly in the pictures provided. Thanks!

They are secured by a leather belt type strap. Have to be unbuckled in order to access them. Don't put something like a phone there that you need to get to quickly!

Q: what are the outside dimensions of the medium bag?

15 inches by 3.5 inches. I have a MacBook in mine and it fits fine with cords and all. It also has functional pocket in the front and side and it is real leather. Im happy with my purchase.

Q: Would I be able to keep a reuseable water bottle in the side pocket of the 13" or 15" bag?

Just received the 13" bag - a 500ml disposable water bottle is a very snug fit. Just disregard the ridiculous leather flap & pocket buckle strap - they just get in the way (and I may decide to cut them off).