Bruises on children

Thanks everyone for your advice! The child was happy at pick-up and didn't even want to leave the playroom...the father seemed relaxed (it is the mom who seemed on edge this morning...understand ably). The bruise is not exactly where Playfelt said it would be, but up higher almost near the top...but it could have happened from falling on a mega block as he is in pull-ups and there isn't much padding (at home he is in underwear as he is trained pretty much at home...so even less padding). I did think of what Playfelt mentioned...the parents could possibly be worried about what I will think...in the same email they explained that their younger child has a bruise on his head from pulling a gate down on himself (he is with me too)...so they do understand that accidents happen. I didn't feel it was an accusation at all, but it still made me nervous. I did respond right away to their email explaining that I wasn't sure, btu it could have been that he had fallen on a toy on Friday when he took a small tumble. I also brought it up at drop-off this morning as I wanted to guage their feelings about it (which don't show in the email) and again they didn't seem accusatory and the dad said it looked like he had fallen on a toy (again I think the mom is more nervous...I understand this). I will think about whether to now leave it alone or raise the topic again...maybe it is better to let it be at this point....I don't want to appear overly concerned or defensive either!