We explore the acoustics of Greek voiced stops produced by 2~3 year-old Greek-acquiring children and compare them with adult patterns, in order to understand developmental universals in the mastery of phonation-type contrast. A truly voiced stop (with negative VOT) is a difficult sound due to aerodynamic requirements of glottal gesture. Prior studies show that French or Thai-acquiring children are hindered by this fact, not mastering them until age 5. To assess the effects of such physical constraints on acquisition, we examine the acoustics of Greek voiced stops and investigate how Greek learners deal with articulatory difficulties of producing them. Greek data were recorded in two experiments and were analyzed in terms of amplitude change during the closure and around the burst. Results suggest the very detailed phonetic descriptions of phonetic categories must be taken into account to provide properly nuanced prediction about developmental universals.