I noticed that my 9mth old baby has been coming home with occasional bruises from infantcare. I checked with the teacher and she got very defensive and said that she;s not sure how he got it. What do you think I should do?

Absolutely talk to the principal about this, ask for reports, photos, CCTV footage. If there are no reports and no conclusive evidence, it means that the school is not attentive enough nor is it caring for its students enough. If they had noticed it, they should have come to you first about it. You can always leave and find a new school!