With all due respect, in my world, that is not professional attire. Again, I fully understand being comfortable and able to interact with the children, but being a former teacher, I think that the entire profession needs to take a hard look at the image they portray.
Many of the parents of the children do have to wear suits to work every day. Seeing someone in capris says that they are not in a professional position. I think it hurts what I think is one of the most important jobs we have to minimize the professional nature of being an educator. In the real world, image is very important. People will respect those who have a professional demeanor more than those who are wearing casual clothing, it may not be fair, but it's human nature.
I think that polos and slacks, or a blouse and slacks or a skirt would be fine. Flip flops are not safe no matter who is wearing them, but more importantly, they're beach attire, not business attire. Just my opinion.