Also, I'm pretty sure even babies need to have a passport in order to get into other countries.
Were these two married at all ever?
Was there any sort of court order ever given regarding this kid, or custody arrangements, or divorce proceedings or anything?
If this is a case of a married couple with their kid where the dad decides to take the kid with him to the UK (8 months isn't a vacation, and any lawyer/judge/cop will agree) to move there, it gets a hell of a lot more complicated, but as Pofecker said, she needs to file for a divorce and most states (not sure about Florida) will allow you to file because of abandonment. That's a pretty open and shut case right there, not to mention as soon as she starts the divorce proceedings, it's up to the judge to determine what kind of custodial arrangement is best for the kid while the divorce is going on.
The judge has to decide what is best for the kid, if he's only a year old, he won't remember much about this, and the judge might order him back immediately, in which case, the British authorities will step in.
Which brings up another question, is the kid a U.S. citizen? Or was he born in the UK, parents came to the US, then the dad and kid went back to the UK? If that's the case, it gets a whole lot messier.
