My DS used to go to a nursery with a good Ofsted report but, despite that, I never felt comfortable.
I agonised for weeks over whether to move DS, as I wanted to be sure that I had sufficient justification (beyond a sort of mothers' instinct) to uproot him and risk his happiness.
DS was scratched twice whilst at the nursery; whilst I realise that accidents do happen, the first incident was not drawn to my husband's attention when he collected DS and the second incident, which involved a nasty scratch and red mark very close to DS' eye, was, so my husband was told when he asked for further information, caused by an older child (possibly from another room as DS, although a baby, mixed with older under-twos on a regular basis).
In the end, I was able to identify my concerns (not just the scratching incidents) and the final decision was easy to make. DS is now at a smaller, very caring nursery, where he is happy and DH and I are entirely comfortably leaving him in their care.
If you are concerned about your DS' nursery and are having second thoughts, as well as talking to the staff, try calling round at unexpected times and observe what is happening. Hopefully your concerns will be resolved, if not, do not feel bad about looking at other nurseries.