I didn't know that Laurence Fishburne's son played the young Bill Foster

Well, that saved the production a few bucks!

I wonder if the presence of a lookalike son had any effect on the casting?

Same trick they did for Shawshank Redemption with Morgan Freeman's old mug shots.

I saw a few articles make mention of this. Personally, I had a hard time believing that de-aging effects weren’t used for this flashback scene because that face was 100% Fishburne’s. Even the gap Fishburne has in front of his teeth is visible. With that in mind, more than one of these articles mentioned that there was no CGI used for this scene with young Bill and Ava, and I thought.... really? Come on, his son isn’t that much of a dead ringer to him.

After stumbling onto an article that gave further details on how the de-aging in this movie was accomplished, turns out Laurence’s son did play young Bill. As expected, he physically acted in the scene but Laurence’s younger face was later projected onto his son’s body. Needles to say, there was digital trickery involved. This also is exactly how they recreated young Douglas & Pfeiffer.... Younger actors were brought in as stand-ins for the legends (Pfeiffer’s actress interestingly played Jane in the first movie’s flashback scene) with their movements being used for 1980’s Hank & Jane. And as you might’ve guessed already, de-aged faces of Douglas & Pfeiffer were then convincingly projected onto the younger actors’ bodies.

Yeah, impressive. Not counting MCU films, the last film that notably did this was Blade Runner 2049 with Sean Young being brought back as Rachael. It’s all so surreal.