"The children are singing songs on the bus."
Translation:הילדים שרים שירים באוטובוס.
Every language has its own prepositions for every case. We can't translate everything literally.
Let's take the verb "to use" (להשתמש) as an example. This verb uses the preposition "ב" (in). e.g. אני משתמש במחשב (I use the computer).
Would you use the literal translation? (I use in the computer).
That's the reason why we don't accept it.
Furthermore, if you use the translation "על האוטובוס", it's more like "the children are singing songs about the bus", which has totally lost its meaning.