Shantae is family-friendly... if you're okay with revealing outfits.
The game itself has almost no offensive content. The only thing that may offend some people is the way the females dress. Shantae, the protagonist, is really the only one who gets a pass because she dresses like a genie. However, Risky Boots has breasts almost the size of her head and wears a skull-shaped bra that shows off her cleavage and tight pants. Rottytops wears a tanktop that shows off her cleavage. Sky wears a shirt that shows off her--- are you getting the picture? Literally every female wears a top that shows off their cleavage. However, it's handled in a non-sexual way. The women just dress like that. Nobody comments on their clothing or body; that's just their design. Later on in the game, some female characters get captured and wear outfits that look almost exactly like Slave Leia from Star Wars. This is the only time in which their clothing is mentioned, but, even then, it's not sexual at all. They talk about the clothing as if it's fashionable and not just a skimpy metal bikini.
So, overall, the only content that could be "inappropriate" is that the females all wear clothing that often exposes the stomach and cleavage, but it's non-sexual. As long as you're not super uptight about that stuff, this game is 100% family-friendly.