Isabella of Valois
You're six years old and you live in the Louvre in Paris. What an intriguing childhood you might have in amongst the glorious works of art and historical artifacts. But it's the 14th century, the Louvre is a cold and draughty fortress and your Dad is known as Charles the Mad. As luck would have it you don't hang around too long because you're swiftly married off to King Richard II of England.
Now as the oldest surviving child of your parents you'd think they'd want you to hang around for a little bit longer, but good relations are always much more important than a good healthy childhood. And this was the fate of Isabella of Valois (and if the idea of a child bride marrying a 27 year old widower grosses you out, then the date of their wedding will come as no surprise - Halloween 1396.
Was this shrewd of Richard? Was it perverse? Of course Isabella was too young to bear children and really solidify things, but if you are a closet homosexual (as was suggested by Thomas Walsingham) then it's a very tidy plan indeed. The wedding went beautifully (if you discount the two ships that sunk in the Channel and the people that were crushed to death in the crowds between Southwark and Kensington) and the two settled down into wedded bliss. In two different locations. Isabella lived in Windsor Castle and Richard would visit regularly and entertain her and her ladies-in-waiting with jokes and magic tricks.
Moonlighting as a child entertainer wasn't to everyone's tastes and certainly not to his cousin Henry's, who ended up locking him in The Tower and starving him to death. The now King Henry demanded the Isabella marry his son, but Isabella as a plucky ten-year-old ,with all the front of a self-hating and cynical teenager, told him to stick it, legged it back to France, married an 11 year old and died in childbirth at 19.