Y'know, now that I'm thinking about it, I don't think I've ever seen more than one 'childhood friend' character compete for a love interest in a romance before.
In Osamake ("A Rom-Com Where the Childhood Friend Can't Lose"), the whole premise is that every love interest is a childhood friend.
The joke is on us though because it sticks to every other dumb harem trope, and it seems like it'll never get anywhere. So in fact it seems everyone (including the audience) loses.
In addition to the other examples given, I can also think of Onegai Twins where the scenario is that the MC had a childhood friend and the characters don't know which of the two love interests it was. (The other is his sister, so...it's not great.)
Anyhow back in the 90s and early 2000s, it was actually a given that the childhood friend won in the end; it's odd the trend reversed at some point. As a result, a lot of love comedies from that era do involve multiple childhood friends, because otherwise it was too obvious who would win.