CC Ādi 2.98

aṁśa-śaktyāveśa-rūpe dvi-vidhāvatāra
bālya paugaṇḍa dharma dui ta’ prakāra
Word for word: 
aṁśa — of the plenary expansion; śakti-āveśa — of the empowered; rūpe — in the forms; dvi-vidha — two kinds; avatāra — incarnations; bālya — childhood; paugaṇḍa — boyhood; dharma — characteristics of age; dui — two; ta’ — certainly; prakāra — kinds.
Translation: 
“His incarnations are of two kinds, namely partial and empowered. He appears in two ages — childhood and boyhood.
Purport: 

The vilāsa forms are six in number. Incarnations are of two varieties, namely śakty-āveśa (empowered) and aṁśāveśa (partial). These incarnations also come within the category of prābhava and vaibhava manifestations. Childhood and boyhood are two special features of the Personality of Godhead Śrī Kṛṣṇa, but His permanent feature is His eternal form as an adolescent youth. The original Personality of Godhead Śrī Kṛṣṇa is always worshiped in this eternal adolescent form.