There is a difference between attending an open evening as opposed to a private visit. On an open evening there may not be children around but you will get a talk from the head and be able to see the classrooms. On a working day visit, you will be able to drill down and ask more pertinent questions. You must be aware though, that Heads are extremely busy and some teach. They are never going to be available to meet and greet 60 parents who want to do separate visits. Often the school secretary will do a tour.
You can look at how the teachers engage with the children. Are they learning? What are they doing? Is it play based education and how does the school structure it's more formal learning in subsequent years? Is this what you want? Are the children busy and are they happy? Are the classrooms inspiring? Is it a place where children enjoy learning? Would you like to be a child in that school? Would it inspire you? Is the curriculum exciting?
I would rather avoid asking Ofsted questions. Schools can put their faults right but then fail to notice other things going wrong. You are unlikely to spot that. However, do read any recent ofsted report and ask to see a synopsis of the development plan showing how they will tackle any issues. If the school was rated inadequate, be aware there is no quick fix.
Also, do not assume children bully each other. Mostly they do not. Most children enjoy school. You are unlikely to know what a school does regarding bullying until there is an incident. You will need to have faith in the head. Do they fill you with confidence? Look at the progress the children make. Education is not totally results driven, it is progress driven.
Lastly, can you see your child at the school. Will they fit in? Do the children seem like yours? You might also look at the reading scheme, library, how they teach maths etc.... but how long have you got?