I dont think you are being stupid. Changes always raise doubts. But if your school is a good school now and they manage well and the children are happy it will probably be ok. There will always be hiccups at first I expect because there are bound to be situations that were not accounted for but if they are that good then they will work it out. What about staff arrangements? More helpers involved in the lunchtime shuffle. I would find out for reasurance what staffing and rota proceedures are in place. I would get all the facts before starting to worry.