I think its unlikely a baby could grow as Regina’s body was stuck in time, but Cinderella’s baby was not “from” the Land Without Magic like Henry, so not sure about that. Baby Henry grew up, so is it just that Henry could grow during the curse because he is special and Henry? Would Owen and Kurt have grown older had they stayed?
I like the poison curse that is out there, as I think Cora cursed George’s wife, and maybe Regina too. It could even be a tragic mistake thing, where Cora made it to curse George’s wife, but Regina had some too.
Perhaps that was what Regina wanted with a mermaid? Maybe she wanted to get some Nostos water but couldn’t get anyone to get it for her.
“If I had a world of my own, everything would be nonsense. Nothing would be what it is, because everything would be what it isn't. And contrary wise, what is, it wouldn't be. And what it wouldn't be, it would. You see?” -- Lewis Carroll, Alice's Adventures in Wonderland & Through the Looking-Glass