To the OP
tell your inlaws that you dont like them doing it and dont find it funny that they are purposely scaring your child for their own ammusment tell them you find it sick and revolting and that if they carry on then you wont be letting them near your child till they can show your child the respect he/she deserves ( sorry cant remember if you have a son or daughter ) as a human being.
I would be livid if people made my children cry on purpose for their own entertainment, does that mean i dont do things that make my children cry sometimes NO but i dont find it funny when they do cry either ( although sometimes ds1's tantrums are drama worth an Oscar and make me smile ) as a mother i find it hard to hear my children cry it sends a reaction through me and at times with ds1 when he had colic i just had to leave him with DH and go out caus i was getting so upset and unable to help him by being upset it was easier to leave him with DH ( i dont know how my husband does it but the crying doesnt bother him the way it does me )
Ive used CC and CIO before and had vaired results with each child but its not easy or fun to do at all its heart wrenching and painful,
anyone messing with my kids had better watch out caus i'll be after them