Hello Heather and welcome to Rootschat.
I can confirm that this headstone is in Cambusnethan cemetery, the plot reference is Section E No.10.
I have some of the burial records, mostly Victorian, here's what I've found. All are in E10.
JANET R ROBERTSON. Newmains, aged 2 years.
Parents - Thomas Robertson and Agnes Ross.
Interred 19th February 1898.
JANE R HENDRY. Stane, aged 15 months.
Parents - Donald Hendry and Christina Robertson.
Interred 29th January 1900.
JOHN ROBERTSON, Newmains, aged 4 years 9 months.
Parents - Thomas Robertson and Agnes Ross.
Interred 3rd November 1906.
I don't have any of the later records but at least this confirms the grave number. It looks as though the age for Janet could be 2 1/2 on the stone, not 21.
In the 1922 street directory 261 Cambusnethan St is occupied by J McGhee but there is a T Robertson at 273. In the 1925 directory the householder at 273 Cambusnethan St is T Robertson, cement worker. The row of houses that included these street numbers was called Hermon Place.
Good luck with your research and if you know the parents of Thomas and Agnes I could look for them.
(The village of Stane is now part of the town of Shotts, a few minutes drive from Wishaw)
Lodger.