hello..i want to ask you guys...suppose that my son playing with some thing...like toys car or car toys? please correct me

then suddenly one of it part is detached or seperated from the car toys...then how do you call it...it comes off? it fall off? (fall off it sounds like it fell down...) like in the other moment..when he is walking..and his shoes is suddenly just come out from his tiny feet because he is still 1.5 years old...what to call it...? your shoe is comes off? or like ur shirt button..one of the button is detached..how do you call it? can we use comes off again ? what is a good word of that?
i need to make a word that simple for him and universal..so evertime something is loose or seperated from it's main he will use that word....
thank you for helping guys ..very much appreciated