I have been doing some research recently into passwords that are reasonably strong, but still memorable enough for younger children to be able to use. Here are a few websites I have found that might be useful to teachers of younger children:
Dinopass – generates simple, pronounceable passwords using words and numbers. There is an option to go for more secure passwords that include special characters as well.
LastPass – this popular password manager has a page where you can check the security of passwords.
WarpConduit’s password generator – these are not memorable words, like Dinopass, but they are designed to be “pronounceable” and thus easier to remember than random strings.