
Now fertility connotations aside, the Maypole is an entertaining and fun activity for children. And for those that don't want to, or don't have the means to erect a giant pole in their yard, there is the mini Maypole. http://www.mppl.org/kids/maypole.html
In my opinion it is not necessary to explain it all to children who are to young to understand the sexual connotations. But older children, and this is completely up to your discretion, could be told some of what the Maypole means. And in fact could probably use this occasion as an opportunity to do magick with you for things that they need in their life.