This statement appears to contain all the information which was in the note so presumably it was written in the receptionist's native Portuguese.
http://mccannpjfiles.co.uk/PJ/LUISA_COUTINHO.htm "When questioned, she confirms that the man was not the father of the girl but one of the members of the group whom was often seen in his company.
The man justified his request by saying that the group had many small children whom they would leave alone when they went to dine. She said that at intervals some two parents would go to the apartments to see if everything was OK."
The deponent made some comments about the request, saying that the Tapas received many requests and that MW only had a quota of 20 per day, but upon the insistence of the guest she managed to make the bookings requested.
Amaral's version in his book of the note is slightly different:
"During the parents’ dinner, the children again sleep alone. A restaurant employee notes on the reception register that certain members of the group get up in turn to go and make sure they are OK."
It is clear something was written in the booking register. If it was written in Portuguese then that pretty much excludes most of the English holiday-makers dining at the Tapas from understanding what the note said, had it been on public display.