I'm not sure what words you found, but if they had (m) next to them, that only means their grammatical gender, not their actual sex.
The most common words for child are generic for both sexes, like leanabh (baby), pàiste (young child).
Lullabies are sung to 'mo leanabh', whether boy or girl.
When they're a bit older, you would say balach (boy) and caileag (girl).
Forms of address: a bhalich, a chaileag. (lad, lass)
Having said that, you would probably call them 'm' eudail' and 'droch isean' most of the time: pet or wee brat!
And adults would use 'thu' to a child, and children 'sibh' to an adult, including older relatives - traditionally. No longer necessarily the case.
Thèid mi leis na siùil-mhara