I haven't read thru everything, just the first page.
I have crate trained 3 dogs pretty successfully. I even crate trained an older dog who we got from the shelter. He was house trained, but not at our house.
Anyway, what worked for us -
*You keep the area in the crate for only as much room as they can turn around section it off and increase the amount of room as they grow or until no longer needed.
*They come out of the crate and directly outside - no waiting. If they do not do business then they go back into the crate for 10 min and the routine is repeated until they do their business.
I keep them on a leash otherwise they can think it's play time.
*Once they do their duty, they can then have free time. During free time it should be confined to whatever room you are in and supervised. If they are playing and suddenly stop then it's time to take them back out or if they start swirling around in circles it's time to go out like immediately. Generally, its good advice to take them out every 2 hours. One of ours has a tiny bladder and she needed to go out more often - so use your judgement. They also need to go out immediately upon waking.
*If you cannot supervise, they should be crated. One it will cut down on accidents and chewing unwanted things. The length of time they can be crated increases with age, I cannot recall off hand. The puppy can remain in the crate throughout the night. However, they do need to go out at first to learn that they will be cared for. Again, they can learn that if they cry - momma comes running. So, you have to realize if it's a real cry for potty needs.
*Provide the puppy with lots of chew toys and if you see them chewing something else, immediately replace that with a chew toy.
*So, with that said, a 5 yr old should not solely be responsible for the training of the puppy. In fact, until you can trust the puppy is potty trained, I would take them out myself unless the 5 yr old is supervised. I had older children with my one dog and we had some issues, so I would not put the stress on a 5 yr old - sometimes puppies look like they pottied but didn't. Or it can just become play time - puppies tend to see children as peers.
This is not to say you won't have accidents, because they will occur. Just clean them up with an enzymatic cleaner to get rid of all traces of odor. Do not reprimand the puppy. Instead, if you catch them in the act, just say "no" firmly, but not harshly followed by "out" as you are rushing them out the door.
"Let's go out" is a good phrase when you are taking them out, but whatever you use be consistent.
When they are in the act of business once they start, you want to say a command word like "go pee" or "go poop" or "hurry". Whatever, but it's a short command and they will eventually learn the command.
As well, as soon as they finish, a high PRAISE is in order. Some use treats and I did for the young puppy, but not for too long and always make sure they've actually done their business (why I also advocate for this to not be solely the responsibility of the 5 yr old). Praise generally works the best.
Also, and this is just my two cents (and been there done that) - raising a puppy is like having a baby and so now you have 2 babies in the house. It is a lot of work for you. I actually had to give up my first puppy because I did not realize as a 20 something how much work puppies were in addition to having a baby plus i was in college at the time (what was I thinking?) The good thing is is that puppies grow fast and learn quickly and really want to please their human caretaker.