I have just posted a photo from 1976 in the Gallery. It shows Henrietta with two of her youngsters on the lawn in front of the Ape House with Mike Colbourne.
I had thought they were Oscar and Henrietta, but the smaller one is probably Julitta. Perhaps all three were there, but I don't remember more than two and I think they would have needed another keeper present. Anne was very tame, so I guess they would babysit her infants to allow her back in with Henry, which would explain the relatively short interval between the second and third births.
Alan