Verb

kwanza (verbal noun of the ku class)

1) Infinitive of -anza

Usage notes

The form -a kwanza, which literally means "of the beginning" is used for first. See Appendix:Swahili numbers for more.

Ordinal numbers

Ordinals are formed by using -a ‎(“of”), which must agree using the verb prefixes with the class of the noun preceding it, followed by the number in question. The two exceptions are -a kwenda ‎(“first”) (kwenda is the infinitive/gerund of -enda ‎(“to begin”)) and -a pili ‎(“second”), which uses the counting form.

From Wiktionary:

https://en.wiktionary.org/wiki/kwanza

https://en.wiktionary.org/wiki/Appendix:Swahili_numbers

What does the "wa" indicate in this sentence? Could I also just say "Mtoto kwanza"?

I see that Swahili follows a logic similar to that of the Romance languages,

I see that Swahili has a similar logic to that of the Romance languages, Wanafunzi wa Mexico Estudiantes de México

while in english it would just be mexican students

Can this phrase be used to also mean the first (born) child in a family?