"A little boy"
Well, not really. Both 'chłopiec' and 'chłopak' used to be diminutives of 'chłop' (peasant, farmer), with 'chłopiec' being in fact the older word and 'chłopak' coming from the Masovian dialect and becoming more popular recently. I wouldn't say that 'chłopiec' sounds particularly cute to me.
The diminutive of 'chłopiec' is 'chłopczyk' and of 'chłopak' - 'chłopaczek'.