Yes, I remember reading that Channing and Streisand were great friends until Streisand and her agent "conspired to rob me[Channing]of my baby!" (this is from Channing's difficult-to-read autobiography--an argument for the importance of ghostwriters and editors, IMO.)
Whatever the true backstory, I'm going to fly against received wisdom. Streisand is the only source of interest in the "Hello, Dolly" movie. She's charming, funny, and sings beautifully. The action around her is staggeringly overproduced, overstaged, and oversold, with almost every performer misused (Tommy Tune, Michael Crawford). The "too young" argument is like the charge levelled at Liza Minelli in "Cabaret" (it was said she sang too well for a woman who was supposed to be a second-rate bar singer). It's a technicality that doesn't matter to audiences, only to bitchy theatre queens.
I ask in all honesty/What would life be?/Without a song and a dance, what are we?/So I say "Thank you for the music/For giving it to me."