Rian Johnson replied this when asked if the movie was okay for a seven-year-old:
"It really depends on the 7 year old. There are intense things in the movie, but I don’t think anything worse than in the OT or prequels."
https://www.cnet.com/news/star-wars-last-jedi-appropriate-for-kids-director-rian-johnson-george-lucas/

I’d really be surprised if it was any worse than Rogue One. It’s weird that they’re advertising that it has intense scenes, though. Assuming Rian Johnson was telling the truth in his tweet, two possibilities are in my mind:

Intensity might be referring to things that we as adults aren’t bothered by, but kids might take very seriously. For example, we might see Luke or Rey getting tortured horribly, and while it wouldn’t make an adult blink an eye (it’s nothing even close to R rated material), to a kid it might be kind of a traumatic to see someone getting tortured like that. I’m sort of thinking of the shot in the trailer where Snoke is kind of bending over Rey with the force.
Disney got some complaints about how violent and sad Rogue One was, especially in comparison to mostly lighthearted (and also PG-13) TFA. I mean, yes TFA had action but it was a cartoony sort of action. Rogue One was a flat out war movie.