As pointed out below, if you are still under your inspection contingency time period you can easily resolve this. If you are not, it gets more complicated. You can cancel the deal, but the sellers may not agree to give you your money back.
I suppose one could argue that a neighbor with a pit bull is a material fact that should have been disclosed, particularly if you have children, but you'd need an attorney's opinion on whether that would stand up or not. You might try having your agent tell the listing agent you're going to back out and why and see where that leads before taking any steps that might cost you more money.