Is it permissible for my eight-year-old daughter to participate in school celebrations, especially if it involves wearing men's clothing such as military and police uniforms, and a thobe and shmagh, and participating in a parade around the school?

Children at this age are not held accountable, based on the Prophet's (peace be upon him) saying: "The pen is lifted from three: from the sleeper until he awakens, from the child until he reaches puberty, and from the insane person until he regains his sanity." So, if your daughter participates in celebrations that include things contrary to Islamic law, she would not be sinful. However, parents must protect their children from anything that might accustom them to committing sins, as children are a trust given to them. Some scholars have prohibited guardians from dressing a child in gold and silk, though this is a matter of scholarly disagreement.