"large and thriving," 1560s, present-participle adjective from chop (v.). Compare strapping, whopping in similar sense. Chopper "a stout, lusty child" is colloquial from c. 1600.
chopping. An epithet frequently applied to infants, by way of ludicrous commendation: imagined by Skinner to signify lusty, from cas Sax. by others to mean a child that would bring money at a market. Perhaps a greedy, hungry child, likely to live. [Johnson]