You know, I think it would be funny if at some point the parents get upset with the kids fighting that they dismember the two kids down to the basics.

No arms or legs, sealed urinary and bowel tracks, no eyes so neither child knows that the other is in the same predicament, and no tongues (temporary), the tongues could be returned for short term use for the kids to answer and the be removed again. The ears will be cut off and replaced like the tongues so the kids could hear the parents.

Another scene we could see down the line would be the parents enjoying a night out and experiments while also having sex.