Translation:We are loading the bicycles into the car.
I'm sorry, SorrisoMW, but your explanation is just plain wrong. In a "where" question the reply is ALWAYS in dative:
- Wo bist du?
- In meinem Haus. Im Auto. Am Meer. Auf dem Sofa. etc. etc.
And so is artischocke's claim that "in" would be a dative preposition. It isn't. "In" is a so called "Wechselpräposition" and it changes between accusative and dative, depending on the context. If the question is "Wo/Where?" it takes always the dative, but if the question is "Wohin/Where to?" you need the accusative ("Ich gehe ins Bett", "Ich fahre in die Stadt").
In this case it isn't that clear if it is "wo" or "wohin", but when there is also action involved (moving something, fitting something into something or anything like that) it is usually also accusative (at least I can't think of an exception). Another example with different verb, but a similar scenario:
"Verdammt! Meine Schlumpfsammlung passt nicht in den Koffer hinein!"