"The children eat chocolate before the dinner."
Translation:Itheann na páistí seacláid roimh an dinnéar.
an wouldn't cause eclipsis in that position either - Itheann an páiste. Páistí isn't eclipsed because there is nothing to cause eclipsis of the subject of a verb.
Plural genitive nouns are eclipsed after the plural definite article na:
biachlár na bpáistí - "the children's menu"
cé atá ag tabhairt na bpáistí ar scoil inniu? - "who is bringing the children to school today?"
Feminine nouns also use na for the SINGULAR definite article in the tuiseal ginideach - these nouns are not eclipsed:
biachlár na bialanna - "the restaurant's menu"
ar nós na gaoithe - "like the wind"
Why do you think that's complex?
Pretty much every other Irish sentence that you've encountered has the verb before the subject before the object, so itheann na páistí seacláid shouldn't cause you any problems.
"before the dinner" is, as you point out, a simple, word-for-word translation roimh an dinnéar.