Four children with superpowers, possible confrontation with pirates on a ship

I remember very few details of the book I am looking for, but here goes:

• The story in question was a full length book.
• I’m pretty sure it was the first book in a series; I never read anything other than the one book though.
• It was a fantasy book.
• I would say the target audience was young adult.
• I read the book in 2011. I don’t think it was an old book at the time (i.e probably written in the 2000s, rather than, say, the 1980s).
• I believe I read it in a soft-cover volume; I do not recall the cover art.
• I read the book in English, and that was the original language of publication.
• The main characters were a group of children, I believe four in all.
• They were a mixture of boys and girls, probably two and two.
• The children had some form of superpower. I believe one of the girls was very strong, one of the boys was very fast, (though it might have been that the girl was strong and fast) and one of the boys was very smart.
• I have some vague recollection that the strong girl’s name started with "M"; she may have been the unofficial leader of the group (and possibly the oldest).
• The children were brought together by some group to stop some badguys.
• I think there might have been other people with superpowers as well, and these four children were chosen out of a larger group.
• I think one of the boys was very young, and there might have been some controversy about whether to include him on the team.
• I think there was some point in the story where the strong girl visited the young boy’s house, possibly secretly.
• I believe there was some confrontation on a ship, perhaps involving pirates.
• There may have been a point where the strong girl tied up one or two badguys.

I know this is not much to go on….