The letter O is one such alphabet that tests children on getting their circles right when they trace it. They should complete tracing the letter in one go from one starting point. So be careful regarding that. The exercise will also help them trace zero when they start with the number tracing sheets.
You need to click on any of the images above to land on the associated PDF from where you can take a printout. Make the kids read the names of the things starting with o aloud when they are completing the sheets.