Does having a large chakra supply for a child indicate one can potentially gain large chakra supplies for an adult? Does Rock Lee, have the potential for large reserves?
Strictly, no. It also has to do with training, but given that almost every ninja gets good training, and some are just born smart like Sasuke, I think yes. Look at what happened to all the Jinchūriki, despite having those massive chakra reserves, they were killed ( but they had Akatsuki members as enemy, so uhh.?)
But it does gives a ninja a good head start if they have large chakra reserves, as that person, if dedicated enough, can practice and excel at any jutsu because they don't have to worry about depleting their chakra.
Just look at Naruto.He practiced and mastered every jutsu not only because of his incredible dedication, but also because he had Kurama's chakra as well.
Rock Lee doesn't seem to have an exceptional chakra reserve. However, he is an amazing Taijutsu user, having opened 6 gates while being a teenager is an incredible feat.
He might have even surpassed Might Gai, and that is saying something, considering Might Gai fought well against Madara.