I just searched and found a forum post dated February 16 where the poster had their account banned, because they accessed from the same Wi-Fi his brother, who had been "legitimately banned," and Roblox assumed the poster's account was actually the brother trying to dodge the ban. I doubt yours is the same situation, but two accounts on the same IP address may have triggered the bans?

Probably a good thing has happened. Get into #Gcompris or better games!

Definitely for the best:
youtube.com/watch?v=N93Ddz2wWl…

My daughter (11) plays it and I envy you for them getting banned. I wish she'd quit. She says it's turning into a mess anyway with AI garbage and idiots, so the last couple of weeks she's been playing her Switch more, which I'd much rather she be doing.

If you don't mind me asking, what did Roblox say was the cause of the account bans? There should be a message that appears when you try to login or access a banned account stating the reason for the ban.