Translation:The girl is hiding cookies under her dress.
crustulum is singular crustula is plural irrespective of the context
How do we know this is 'her' dress and not 'a' dress or 'the' dress? : We don't know. If 'a' or 'the' is not accepted maybe you should report. Because strictly speaking it could mean any of the three, although 'her' might be implied.
A morally shocking sentence :)
A few quotes on truth and ethics:
«in vino veritas». The truth is in wine (people will say anything drunk).
«veritas numquam perit». Truth never dies (Seneca).
«qui vitulum tollit, taurum subduxerit idem». He who steals an egg will steal an ox.
«animo furandi». With an intention of stealing (a legal phrase).
«dura lex, sed lex». The law is harsh, but it’s the law.
Shouldn't it be "crustulam"
crustulum is neuter. Its plural is crustula.
And neuter words always have the accusative look like the nominative -- in all the Indo-European languages I'm aware of, from Russian to Greek and from Sanskrit to English (where we have "he/him, she/her" but "it=it").
Thus crustula is both neuter plural nominative and neuter plural accusative.