you know just do it gradually. my kids would be a little fussy like that because i would put water in the cup and it was a little strange to them, to be drinking water instead of breastmilk. Your bub will get used to it soon. Just be wary of bub trying to walk around with the cup especially if bub is drinking from it because kids fall all the time and you wouldn’t want bub to get hurt. Just a tip because kids are quicker than you think You guys will get there in time No worries

Maybe your bub is not quite ready for a sippy cup