schuim — foam

Mijn dochtertje schaterde van het lachen om al het schuim in bad.
My daughter burst out laughing at all the foam in the bathtub.

schateren (schaterde, geschaterd) – roar (with laughter)
het schuim – foam

I don’t quite understand why “lachen” is used in the sentence.
1. If it’s a plural form of “lach” then why with “het”?
2. If it is a verb then it makes the translation even more confusing!