I have good news for you! I have also struggled with this same issue and I have some solutions you can use TOMORROW!!!
Tip #1
Use a QR code. Half the battle of getting your kids logged in, is getting them TO Google Classroom. Make it easy for you and easy for your kids use a QR code. All you need to do is add a free QR reader app to your device. ( You can download at the app store). Then create a QR code with QR code generator and boom your kids are where they need to be. Here's a link to a QR generator site.
Tip #2
Give them a Driver's License. Type their name and log in information onto a card and keep it handy. I keep my kids cards in a plasctic bag with their headphones. (Hint: make lots of copies!!!!) You get bonus points if you put the QR code right on the driver's license. Click here. to get my logging in guide with free driver's license( it's editable!!!)
Tip #3
Make sure you use the correct font. Want to confuse a kindergartener? Show them the letter a or the letter g. Even our most competent kinders need a minute to learn what these letters are. No wonder it takes them 20 minutes to log in. Make sure you make it easy for your kids. Write their login in info in the same font. Most keyboards are in Calibri. Look closely at your keyboard, if it's all in capital like a laptop then use all capital. If it's all in lowercase like a chromebook then use lowercase.
Tip #4
Color code! The keyboard can be a confusing miss mash of letters with seemily no order. Give the kids a little help. Place a small sticker, or card at each row to color code the row.
Then make sure you color their login card to match. It honestly takes the sting out of looking for through the entire keyboard.
Need a little keyboard practice? Grab my keyboard resource here.
Grab my FREE complete kit for helping kids log in faster here.