my LO is 3mths now, before that she was perfectly fine with my mother carrying her. now, she cries and scream when my mother carries her. at this moment, my mother can play and talk to her etc but not carry. i’m also very puzzled and sad to witness it. exposure doesn’t really help..my mother has been coming to my place regularly also.
just to share my experience & hope it gets better for u & ur LO... my kids have been alternating between 3 homes (different environment) since birth (including overnight) and there is generally no separation anxiety i suppose because it is their normal...
not only longer exposure, but stick to one side of the family. don't keep switching between your in laws and your parents. babies do recognize people and places at that age and it scares them if they keep seeing variations.
longer exposure to get used to it