Question: Must I have my children vaccinated?

I believe vaccinating children is dangerous

This is not a fallacy, it is just an erroneous (and potentially harmful in this case) belief. Of course, anything can be "dangerous" including jogging. What really matters is weighing the risks with the benefits, and making an informed decision based on the data.

The reason WHY you believe this is likely to uncover many fallacies such as the anecdotal fallacy ("i know this kid who..."), emotional appeal ("This anti-vaxx group showed me photos of..."), etc.

and is also unnecessary for me because all of the other parents have already had their children vaccinated.

I wouldn't say unnecessary, but in an ideal world, less urgent is a reasonable conclusion. The problem is, many parents think this same thing (let the other parents take the risk). As more parents vaccinate their children, the overall risk to any single child goes down. Conversely, as more parents refuse to vaccinate their children, the overall risk to any single child goes up. I see no fallacy in this reason; rather you coming to an incorrect conclusion because of missing information.