Since you say it is right in the middle, do you mean the middle of the quilt or the first row?
Either way I would leave it and do the child's initials in that square. It won't be noticeable if you make them big enough. It will look like you meant to have the initials there.
Don't cry! There is a Chinese proverb that says every project must have an error of some kind so as not to insult the gods who are perfect.
Marie