Try this wording instead: Because Mother's Day was coming (soon), they decided to buy a watch as a present for their mother.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
Vincent TeoCan I say,You need to change these round as
(a) They decided to buy a watch as a present for their mother because Mother's Day was coming soon.
(b) They decided to buy a watch as a present for their mother because tomorrow was Mother's Day.