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There has been a time.........

There was a time............

Also,

My nanny has worked in our household for nine years. (She is not working in our household anymore)

My nanny has helped me once when I was in trouble. / My nanny has helped me once when I was nine.

( I think this is correct, but I saw it in a site that you can't use "has helped" if there's a specific time clearly stating that it's in the past)

My nanny has worked in our household since I was a baby until I was 10.
Correct too?

Thanks
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AnonymousThere has been a time..

There was a time..
Impossible to say without context. Usually, it's There was a time when ...
AnonymousMy nanny has worked in our household for nine years. (She is not working in our household anymore)
This is a little strange. You need one of these:

My nanny has worked in our household for nine years. She still works in our household.
My nanny worked in our household for nine years. Now she doesn't work in our household anymore.
AnonymousMy nanny has helped me once when I was in trouble. / My nanny has helped me once when I was nine.

( I think this is correct, but I saw it in a site that you can't use "has helped" if there's a specific time clearly stating that it's in the past)
No. Not correct. That site is correct. when I was in trouble and when I was nine both indicate a specific time, so the present perfect tense (has helped) is not possible. Omit has, and you'll be OK.
AnonymousMy nanny has worked in our household since I was a baby until I was 10.
Correct too?
No. The present perfect (has worked) can only be used to indicate that the action continues up to the moment you make this statement. That contradicts until I was 10, because you are not 10 now, at the moment you are making the statement. You'll have to leave out until I was 10.

If your nanny left the household when you were 10, you'll have to say it like this, using from and until:

My nanny worked in our household from the time I was a baby until (the time) I was 10.

CJ
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Hi,

There has been a time..

There was a time..

Also,

My nanny has worked in our household for nine years.

(She is not working in our household anymore) So to show it's a completed activity in the past, just say 'She worked . . . '

My nanny has helped me once when I was in trouble. / My nanny has helped me once when I was nine. Again, it's just a completed event in the past, so say 'she helped . . . '

( I think this is correct, but I saw it in a site that you can't use "has helped" if there's a specific time clearly stating that it's in the past)

My nanny has worked in our household since I was a baby until I was 10.

My nanny has worked in our household since I was a baby until I was 10. Correct too? No. Same comment.

Clive