Most people get worried because the hindi words their kids start using have religious significance. Same with the imitation of hindu rites.
It is not merely because the kids used a random hindi word. No it’s because the kids say things like: ‘main pooja karraha hai. Main tumhari aarti utarun’ and etc.
Some people don’t feel comfortable with that and don’t want their kids to do or say that.
I wouldnt be ok with it either. Just like I wouldnt want my kid to start making the sign of the cross, or to say Shalom instead of salaam.