Many children cannot speak a full sentence in their mother tongue. These children did not learn many of those words at home.

Other parents were very particular and "did not understand" what their children were saying unless they expressed their ideas in full English sentences. Their children never played on a mirpeset, never had a metapelet, and never went to the makolet to buy a sakit chalav. They played on the balcony, had a babysitter, and went to the grocery store to buy a bag of milk. (Yes, Israeli milk is sold in bags).

As the parent of a bilingual child, it is your job to develop and use consistent terminology.

You will defeat at least part of your bilingual task if you use the term in the local language for a specific food item or for a part of the house.

No it won't destroy your entire effort, and the child will still be raised bilingually, but your work will be much less effective.

And that would be a chaval.