There is nothing intrinsically “pagan” or “evil” in celebrating All Saints Day or its vigil, dressing up in costumes, playing games, having parties, carving vegetables or collecting candy from willing neighbors. You are free to do any or all of these things if you wish, because none of them are intrinsically disordered, provided that there are no evil intentions in the act.
Halloween is not a philosophy or system of belief, good or bad, but a set of American customs and practices derived from European ones. It should be noted that Christianity has frequently externally borrowed from pagan customs – e.g., wedding rings, brides wearing white, Christmas trees and Easter eggs – but transformed their interior meaning to conform with Christ.
On the other hand, we do not want to use our legitimate freedom to alienate or scandalize our Christian brothers, which would be a violation of charity.
We should not be a stumbling block for others. If your family members or friends choose not to celebrate Halloween, respect their decision and do not do anything in their presence which they would find offensive.
If you choose not to celebrate Halloween in the common customs, you might consider replacing it with a celebration of All Saints Day or adapting the common customs to highlight All Saints Day, such as handing out holy cards with candy or dressing up your children as saints.
Halloween can be legitimate fun, but the decision of whether to celebrate Halloween should be made prudently, charitably and in conformity with the faith. As St. Augustine said, in essential things there must be unity, in matters of opinion there may be diversity, but in all things there must be charity.
— Catholics United for Faith