As others have noted, Sharon has a well-established history killing Arab civilians - men, women and children - in a very deliberate and calculated way. So, it is certainly not impossible that he did this, at least in principle. If Sluizer is telling the truth, it should be possible to establish this, or at least find suggestive evidence. When was Sharon in Beirut? Is it unlikely that he was armed, despite regulations? Has he expressed ideas which suggest that he regards Palestinians as subhuman? The story is worthy of investigation, at least. As I said, we know for a fact that Sharon has, historically, deliberately murdered Arab men, women and children. If he did this, it would just be a continuation of something it is already established he had done in the past.
Jerusalem light rail conductors striking over new train schedule (Haaretz)
from the article: 'I saw Ariel Sharon murder 2 Palestinian toddlers in Lebanon'