Is it normal for photos and videos of babies taking a bath to be shared in family chat groups in an app if it's just family members?

Yeah, it's normal. People have been photographing and sharing images like that for decades.

If you want to be a weird, obsessive-compulsive, pathetic and boring repeater troll spammer, there's nothing we can do about it, but draw the line at being a pedophile. Nobody has any patience or sympathy for that. Don't ask another question about a naked baby or your account will disappear the next day. First and final warning. 

It's not unusual but also not wise. Taking such photos to be seen only by family or people the photographer WANTS to see the photo is fine. Posting in a chat group causes the person who posted it to lose all control over who sees it, as it can easily be downloaded/copied and shared anywhere by any user in such a group.

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Your question belongs in Computers & Internet>Internet>Other-Internet as it's currently in Yahoo Products>Yahoo Groups (Groups was closed for good in December 2020) and not applicable to this subcategory (and thus decreases your chances of getting many useful answers).

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Yeah, it's normal. People have been photographing and sharing images like that for decades.