Parties at home by definition are more intimate and probably more fun to organize. If the weather is likely to be warm you can plan on using your garden as part of the party arena.
There can be complex and sophisticated clues for adults and simpler clues for children. The clues can be incorporated on a place mat for the food for the children, so that they have there own clues to start with. This is easy to do on a personal computer with a drawing program, and they can be made to match the invitations.
Some themes have been done to death such as a Roman togas party, but with a little thought and enthusiasm you can have a party that is different. A Roman God and goddesses party gives a theme that can have an element of dressing up, or a heroes and heroines party. A movie theme can mirror your favorite movies, aliens, romance, and science fiction.
Not everyone has a specific interest that makes a theme easy to choose and it can always be a time. It can be the decade that you were born, the First World War, or the age of steam. It can be a geographical place, such as a cave or a country or a place combined with an era, such as the thirties in Hollywood.
It is fairly easy to bring something back if it is a place. If you have enjoyed a trip to Europe then it is fairly easy to bring a part of Europe to your party.
Paris could be metal bistro tables in the garden, Belgian chocolates, and a plastic London bus. Simple fancy dress is easy with berets and scarves but period costume can be used to make it more formal. Italian or French food is easy as is French music.
The library may be able to assist with some French or Italian operas. Drinks are always easy for a party with a European theme wine is easily available but cocktails are also perfect if the party is going to be short.