  We have studied the young stellar populations in NGC 602, in the Small
Magellanic Cloud, using a novel method that we have developed to combine Hubble
Space Telescope photometry in the V, I, and Halpha bands. We have identified
about 300 pre-main sequence (PMS) stars, all of which are still undergoing
active mass accretion, and have determined their physical parameters (effective
temperature, luminosity, age, mass and mass accretion rate). Our analysis shows
that star formation has been present in this field over the last 60 Myr. In
addition, we can recognise at least two clear, distinct, and prominent episodes
in the recent past: one about 2 Myr ago, but still ongoing in regions of higher
nebulosity, and one (or more) older than 30 Myr, encompassing both stars
dispersed in the field and two smaller clusters located about 100 arcsec north
of the centre of NGC 602. The relative locations of younger and older PMS stars
do not imply a causal effect or triggering of one generation on the other. The
strength of the two episodes appears to be comparable, but the episode
occurring more than 30 Myr ago might have been even stronger than the current
one. We have investigated the evolution of the mass accretion rate M_acc as a
function of the stellar parameters finding that log M_acc ~ -0.6 log t + log m
+ c, where t is the age of the star, m its mass and c is a decreasing function
of the metallicity.
