Renee MacRae was last seen driving out of Inverness with her three-year-old boy Andrew on November 12 1976.
The 36-year-old mother-of-two's BMW was found burned out in a lay-by on the A9 near Dalmagarry, 12 miles south of the city, but the pair were not seen again.
No-one has been charged over their deaths.
Police Scotland, who are conducting a murder inquiry, revealed earlier this month that Leanach Quarry, east of Inverness, was being drained of water to allow police to carry out a forensic search of the site.
It is understood pushchair wheels are among the items recovered so far.
Bones have also been found at the quarry, although these are believed to be animal parts.
Detective Inspector Brian Geddes, of Police Scotland, said: "As part of the search operation at Leanach Quarry, numerous items have been found to date, many of which have warranted further research and examination.
"Meticulous analysis is now ongoing to establish if any of these items would be relevant to the investigation into the murders of Renee and Andrew MacRae."
The quarry was previously deemed too dangerous for divers to enter, prompting the need for millions of litres of water to be pumped clear from the site.
Silt and debris from the bottom of the quarry is the subject of forensic tests at another location.
The police team said earlier this month they remain "extremely confident" vital evidence they believe was hidden in Leanach will be recovered.
In 2004, a full cold case review resulted in a month-long excavation of Dalmagarry Quarry.
Several days were spent at Leanach Quarry last October, when officers released an image of Andrew around the time of what would be his 45th birthday.
A picture of a Silver Cross pushchair, identical to the one used by Ms MacRae for her son, was also released.
It was believed to have been with them when they went missing.