Um, are you serious? And, how do I get it to stop?

On Tuesday and Thursday I watch my neighbors child(ren). Sometimes I have just one, same age as my son, and sometimes I have all three plus my own. For all of you math wizards that comes to four kids, the two older girls come after they get out of school for about an hour. Well today I had two of the three, and mine, and I ask her before she goes off to kindergarten if she needed lunch to which she states she did. So I make sandwiches for everyone and as I'm giving her the sandwich, made with love, she walks out the door and I'm thinking she is eating it on her way to school. Well, when Jimmy went to work a few hours later he found said sandwich on the dive way. She threw it on the pavement! If she didn't want it she should have said so! Not throw it on the ground, how is that acceptable behavior? I know she is in kindergarten, but come on now. I don't want to deny her food if she needs to eat before going to school, but I don't want to waste it either. I should have made the sandwich and right away thrown it in the garbage. I was so insulted and mad and from now on I am going to tell the mother that she needs to be fed before she comes because I don't have a money tree for them to just litter food on the sidewalk. Is that rude of me?
The second issue is while the little boys were playing the neighbor was chasing my son into a corner grabbing his shirt and throwing him to the floor. I was so shocked that I thought I saw something that didn't happen. Until it happened again. I went over to the boys and told the neighbor kid that we don't play like that and to go play with the toys, but when my back was turned he did it again! Three times for those of you counting. I have no clue how to address this with the parents because I don't want them to think I am one of those overprotective mothers that think everyones kid is after hers. That is not the case. I get after my son when I see him treating anyone unfairly. I don't know. Maybe I just need to not watch them. It messes with my sons nap times and if he is just going to get a beat down when my back is turned I can take him to play group elsewhere and he can have the interaction with a bunch of kids whose parents are in attendance. Ah, but then I am putting the neighbor in a bind having to find another means of babysitting. His family was doing it all before and well, they may have to do it again. We will see how Thursday goes, I will keep y'all posted.