Ah, then my initial correction was right, you should have used шли as it was an ongoing action at that time. You see, you're right that ходили implies a routine, habit, but only if the action is not happening now or at a time you're speaking of as ходили implies a completed action in that case.
As @Serge_spb mentioned:
This means that in your sentence they were on their way FROM shopping and not on their way to "shopping", as you wanted to say.Originally Posted by Serge_spb
That's the difference.
I think you tried to do that, but failed due to your yet limited knowledge. No worries, you'll nail these kind of things soon enough and we'll be happy to help you on your way.Originally Posted by grafrich
One thing to note, in Russian невидимый usually means invisible in a sense of not being seen from any angle, in plain sight etc... Special forces kind of invisibility, which is not possible as of now as far as we know. If someone or something can't be seen because they're covered from view by something, then we usually say:
Её/его/их etc не было видно