At the freely available NSW archives online images if the Assisted Passenger list for that voyage, at page 12 of 21, under the section for Widows and their families:
DOUGHTERY
Margaret, 35, Antrim, Ch of Eng, Both (Read and Write)
Alice, 15, Weaver, Antrim, CofE, both
Robert, 14, Labourer, Belfast, CofE, Both
John, 10, no further details.
Likely from your attached snip the child would be John, and likely Alice is listed with Margaret as they are both females charged at adult rates for mess purposes. Likely Robert would be listed separately too, as he too, at 14 would be messed as an adult. I expect your snip is from the images available from the other reels at NSW Archives and made freely available via Mariners and ships in Australian waters website.
JM
This is a small portion on an arrival manifest for the Samuel Plimsoll into NSW Aug 19-1876
A Mother
Daughter
2 sons left are marked clearly as leaving on the manifest .
They arrived inNSW 19 Aug and left a few weeks later they leave on the Dandenong for Victoria on the Dandenong arriving 4 Sept
The mother went missing then and never seen again .
Wondering if we have found one of the children has not arrived into NSW perhaps died en route to NSW butim having trouble working out
Margaret Doughterty -Work woman ( Interesting term ) .
Alicia then " do "
1 child
Is this "do " a ditto for the other child .
It seems odd that they did not record the actual child
If not it may explain the mothers mental state upon arrival in Victoria .
I would load the docs butthey wont load so trying to load this snippet at least