  Context. The Gaia third Data Release (DR3) presents the first catalogue of
full-sky variable Young Stellar Object (YSO) candidates observed by the Gaia
space telescope during the initial 34 months of science operations. Aims.
Numerous types of variable stars were classified using photometric data
collected by Gaia. One of the new classes presented in the Gaia DR3 is the
class of YSOs showing brightness variability. We analysed 79 375 sources
classified as YSO candidates to validate their young nature and investigate the
completeness and purity of the sample. Methods. We cross-matched the Gaia DR3
YSO sample with numerous catalogues from the literature, including YSO
catalogues based on optical and infrared data, as well as catalogues of
extragalactic sources and Galactic variable stars. YSO catalogues were used to
quantify the completeness of the Gaia DR3 YSO sample, while others were
inspected to calculate the contamination. Results. Among the 79 375 potential
Young Stellar Object candidates published in the Gaia DR3 variable star
catalogue, the majority of these objects are distributed along the line of
sight of well-known Star Forming Regions and the Galactic mid-plane. We found
that the contamination level is well below 1%, while the completeness is also
at the percent level, taking into account that the Gaia DR3 YSO sample is based
on sources that showed significant variability during the data collection
period. The number of sources in our sample that were never catalogued before
as YSO candidates is in the order of $\sim$40 000 objects.
