No, she certainly wasn't "protecting" her kids from her father. Her claim that that's the reason for "shielding" her children, it begs the question, "If you were protecting the kids all this time, why didn't you speak to the authorities?" She wouldn't have an answer. A reasonable person, finding out something like this about a family member would speak to the police and also not advertise it in the media right away.
In the majority of these cases if it's a family member, co-worker, friend etc, the person reporting is not named at all. They remain anonymous to the media. It might be reported an aunt, uncle, brother, sister reported the accused. They don't run to the media like the Markles.
Meghan put out the statement about the kids to counter people's questions concerning Tom Sr. not seeing his grandchildren all these years.
The whole thing stills smells to high heaven to me. The police are investigating. Tom Sr. hasn't been arrested or indicted, except by his two family members and the media.