Principal English Translation: 

one's offspring, son or daughter (a necessarily possessed form; see Karttunen); this can also mean small or serve as an affectionate element (see Siméon)

Frances Karttunen: 

-PIL a necessarily possessed form, one's offspring, son or daughter / hijo, hija (S) To mean the offspring of someone, this is used in possessed form, and the plural is necessarily suffixed with plural possessive -HUĀN. Unlike PIL-LI 'noble person,’ this plural does not reduplicate, NOPILHUĀN 'my children' contrasts with NOPĪPILHUĀN ~ NOPĪPILLŌHUĀN 'my lords,' the latter forms rather unlikely without the honorific -TZIN. Honorific -TZIN is generally but not universally used with 'offspring' too, nopiltzin 'my child' (Cf.55v). Although PIL with the sense of child rarely occurs in absolutive form, the diminutives PILTŌN-TLI and PILTZIN-TLI do, and in these the plural stem does reduplicate in just the same form as PIL-LI 'noble person,’ PĪPILTZITZINTIN. See PIL-LI.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 194.

Attestations from sources in Spanish: 

Pil indica...pequeñez y se une a menudo a los sustantivos: oquichpil (oquichtli), hombrecito; totopil (tototl), pajarillo, pájaro pequeño; y algunas veces a los nombres propios: Pedropil.
Rémi Siméon, Diccionario de la lengua náhuatl o mexicana (Mexico: Siglo XXI, 1988), xxxix.