I did some research. 2 posts of 2 movies coming soon (the 3rd I couldn't find). I also briefly checked the novel. Obviously no bibs mentions. He's just described shirtless and with these glasses. Probably it's assumed for a boy wearing bibs in 1940s Georgia. In the novel he's 6yo. In the play script 7yo (like Brandon deWilde). Maybe the boy in the 1982 version isn't 10 yo, but definitely not 6 either. Rather 8 or 9.
I found these great 2 stage plays. Pic 1 is from a 2017 play directed by Karen Jambon, Jago Mystiek as John Henry in long dark brown bibs. Also good sitting scenes. Clip by Taylor Flanagan is called The Member of the Wedding: trailer. Stage: Different Stages, The Vortex Austin Texas. Some more pics in clip radio interview.
Pic 2 is from Actors' Theatre, directed by Peter Alzado, 2018 clip by G. Coleman, Member of the Wedding Actors Theatre (1h37) with an unknown boy in long faded blue bibs. Ashland, Oregon? Maybe filmed earlier (back to 2002).
Another stage play is a 2018 in Wiliiamstown with Logan Schuyler Smith in dark blue shortalls (curly hair), unpictured, pics on web.
Both interesting and long pairs, rating~7 each. And older than 6 as well. But I prefer the 1982 version.
First entry, still rating 7, I also forgot that the boy wearing a dress/tutu near the end and other cross dressing scene.
I found another 2007 stage play (in London SE1, Young Vic) with the tomboy in cuffed up dark blue bibs.
https://biboverallsfilms.blogspot.com/2023/08/the-member-of-wedding-1982.html
