Context : We present the basic ideas and first results from the project we are carrying out at present , the search for and characterisation of pre-main sequence ( PMS ) stars among the members of Galactic young clusters .
The observations of 10 southern clusters , nine of them located in the Carina-Sagittarius spiral arm of the Milky Way are presented .

Aims : We aim at listing candidate PMS member stars in young clusters .
The catalogued stars will serve as a basis for future spectroscopic studies of individual objects to determine the properties of stellar formation in the last phases before the main sequence stage .
Properties such as the presence of residual envelopes or disks , age spread among PMS members , and the possible presence of several episodes of star formation in the clusters , are to be addressed .

Methods : Multicolour photometry in the UBVR _ { C } I _ { C } system has been obtained for 10 southern young clusters in the fourth Galactic quadrant , located between Galactic longitudes l=238 ^ { o } and l=310 ^ { o } .
For six clusters in the sample , the observations presented here provide the first published study based on CCD photometry .
A quantitative comparison is performed with post-MS isochrones , and PMS isochrones from three different evolutionary models are used in the photometric membership analysis for possible PMS stars .

Results : The observations produce photometric indices in the Johnson-Cousins photometric systems for a total of 26962 stars .
The matching of our pixel coordinates with corresponding fields in the 2MASS data base provides astrometric calibration for all cataloged stars and JHK 2MASS photometric indices for 60 % of them .
Post-MS cluster ages range from 4 to 60 Myr , whereas the photometric membership analysis assigns PMS membership assignment to a total of 842 stars , covering an age range between 1 and 10 Myr .
This information on the PMS candidate members has been collected into a catalogue , named DAY-I , which contains 16 entries for 842 stars in the field of 10 southern clusters .

Conclusions :