I wondered if it is possible to switch between two accounts so one can be used by myself as the main account while the other can be used by my child. So can I use that as a potential way to have 2 save files?
Yes, you can simply switch between 2 accounts. The save data will be the one belonging to the account you currently are logged in with.
The only way this could backfire at you is if you'd abuse with either of those, but that always backfires.
It doesn't need to be a Google and a Trainer account though, it can simply be 2 Google accounts if you'd want to.
You can just sign out and sign in to your other account, but beware it is against the Pokemon Go Trainer guidelines posted by Niantic to have multiple accounts, since you will be playing on the same device there is a good chance that they may think you are going against this rule and playing on two accounts.
Don’t do it. Play fair. Pokémon GO is meant to be played on a mobile device and get you outside to explore your world! Methods of cheating, unfortunately, are limited only by cheaters’ imaginations, but include at a minimum the following: using modified or unofficial software; playing with multiple accounts (one account per player, please); sharing accounts; using tools or techniques to alter or falsify your location; or selling/trading accounts.
Even we can run Pokemon Go Multiple accounts simultaneously on any android device but we shouldn't do this to run two accounts at the same time as it could result a ban. However this could help us to switch b/w multiple accounts quickly without logging in or out. So you can easily manage two Pokemon Go accounts for you and your child or any other family member. You just need only first time Pokemon Go login and then no need to login and logout again and again. Here is the method described with Pros&Cons to run and switch b/w Pokemon Go multiple accounts simultaneously without losing game data.