i have sent my 3 year old with the school and they too had a full day thing out in the open. she came back happy and tired and super excited :) i think it will depend on the school overall and how comfortable you have been with them about safety of your child. if you share a good rapport with the teachers you can ask them exact details and voice your concerns. as long as the student teacher ratio is not too vast, i think you can send your child.
you know what...this reminds me of a funny incident. our daughter was supposed to go on a school day trek and she was 4. i was absolutely fine with her going but my husband was flipping out. while the children went in the school bus, my husband actually followed them everywhere in his car, and then by foot! he came back till the school and finally picked her up and got her home. of course the school or our child was not aware of it :)
talk to the school and get full details about the place, what they will do through the day, the area, contact numbers, how they will handle an emergency or safety issue and so on. as long as you feel there are enough good teachers with a certain number of kids, it should be alright.
My sister is know in the same situation. More exactly - our mother. I am trying to convince her that my younger sis will be ok and feel good with her classmates, but mom is worrying. What arguments should I bring her for helping sis?