The are launched from a bash script.
Trying to enter any command on the terminal is not possible because of the scrolling output from these programs.

It still works, even if you don't see; use the copy+paste feature.
killall(1) might help (if the processess execute the same program)

Sometimes its easier to log in using a second terminal.

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Likely, ps aux - to find their process number - then kill -9 <number>

inside the scrolling terminal, have you tried Ctrl+C and/or Ctrl+D?

My thoughts exactly, but considered that maybe they have just the one console.

Therefore some of the other ideas, plus if you know the names of what you started, you can also do: pkill <command-name>

To abefroman's point about a second terminal.

Why are you running a bunch of programs that cause logging to the screen all in the same terminal?

Further note that what you can do instead is the following:I believe this redirects all stdout and stderr to the log file you specify but then allows you to continue in your terminal where whatever program or process you've run is now in the background.