No, the baby is not the assistant. Ryan Choi is the second Atom in the comics, he's asian and he's an adult. The image just shows the subtitles were Ryan was mentioned.
That means Ryan didn't appear visually, he was just mentioned.
Yes, if a character is mentioned only in a movie or TV series we just grab a screenshot of the subtitles. Considering the big "Mentioned only" at the top, the presence of subtitles in the image and the text corroborating what the subtitles say, it should be blatantly obvious that the baby is not Ryan Choi, nor a lab assistant.
The image is still a bit misleading tho. For example, the "Mentioned Only" template doesn't even show up in the mobile version. I don't think the subtitles are complete, it seems like the screenshot was taken before the full line was written. I don't know what they say after "your", but maybe the rest of the subtitles can be more clear about it.