I would think 3 liters would be plenty. But I guess that depends on your area; if you live in a desert climate, probably not. I live in a province with over 100,000 lakes, most of them where I live; so I'm not worried about finding water.
I think hydration bags are good, some are strong; others are not. Buy quality. I've liked the 4 out of 5, that I have owned. The 5th one, was one I ordered off of amazon; it was a cheap chinese one, I bought it for the carrier. The hydration bag leaked as soon as I put water in it.
That's great! My doughter has the strength but still lacks the discipline (expects me to carry everything). As I said she's 4. Maybe I should put more attention into training her, I thought she was too young for it.
Fill up a bag, with the necessaries; include some small comfort items/toys and say here, carry your own stuff.
My son has never had a problem with carrying his own gear, he's being doing it for 8 months now. He knows when we start getting dressed to go outside, to grab his bag and put it on. He picks up on things really quickly though, we didn't have to train/teach him.
my 3 year old loves to carry a camelbak backpack. He loves to load it with snacks and for some reason loves to drink out of a tube. We just went hiking about a mile this weekend.
The two things I would add would be
1) the universal silicock key that lets you open any commercial water spigot (on schools etc)
like this one
https://www.amazon.com/Jones-Stephe...1476631489&sr=8-1-spell&keywords=silicock+key
2) change out the nalgene for a sawyer water bottle filter. like this one
https://www.amazon.com/Sawyer-Produ...476631592&sr=8-1&keywords=sawyer+water+bottle
or an inline sawyer mini/point one that you can plug into the line of your camelbak to fill it
https://www.amazon.com/Sawyer-Produ...45&sr=8-1-fkmr0&keywords=sawyer+mini+camelbak
^This is some real good advice.
I carry a 1qt stainless canteen, with the cook cup/lid; as well as a 2 liter hydration bag (sometimes) and have a sawyer mini, along with some water purifying tablets.
Also, kids love drinking from hydration bladders; I think they think it's cool. My son likes to use mine all the time.
I like the hard bottles myself because my GHB is constantly being moved from the car to the house back to the Jeep and back inside, etc. I've got a Platypus that was nearly puncture simply from constantly being moved and shifted and smashed. Plus, my canteen has a metal cup for boiling.
Stopping to drink also gives you a chance to pause and observe surroundings and listen for sounds. It's important to stop if possible every so often for at least five minutes. Most adversarial entities will not go a full five minutes without moving or making noise. So if you can pause and stay fairly quiet for at least five minutes at a time, dangerous situations can be seen or heard ahead of time.
^This is the same with me, I like my stainless canteen a lot and my sawyer screws right on it. Mine also has a cup, that I use to cook with as well. Multi-purpose items, are the best items.
I carry my GHB, as my EDC. It could even serve as my BOB, if need be.
You can keep a water bladder filled for awhile, I've been told up to a year as long as the original water is relatively clean. Just make sure to clean the bladder with some water/bleach before you fill it and don't drink from it prior to storage as bacteria from your mouth will be the main culprit of making your water bad.
Source hydration makes some very strong bladders, someone linked the one I have above. It's a bit more expensive then camelback, but worth it imo.
I use mine all the time, but if I didn't I'd probably clean and fill it every 4-6 months and just keep it in the bag. It can take a beating, but I would avoid putting a lot of weight on it unnecessarily, especially if it's just sitting in your closet or the back of a vehicle.
As a backup I keep some iodine crystals in my bag to purify water.
Yup, I keep mine filled as well. But I also use it a lot, nearly every day.