That specifically relate to children, lady
However the thread title says "should it be illegal for first cousins to marry?"
Now, the reason we do not feel any sexual attraction towards siblings we have grown up with and by default to cousins is to do with a genetic predisposition if you like - it protects us against incest. People who have grown up with cousins may well view them the same.
But it is not the case for everybody. Studies have estimated that one in five children live with a man who they believe is their father who is not. If you think about it, assuming everyone stays local, there is a strong chance of the siblings meeting and beginning a relationship.
I would not personally recognise my two cousins if I walked past them in the street.
Furthermore, marriage doesn't equate to children. Banning a legal union between siblings and cousins won't stop children being born to them.
If your real, genuine concern is for the children and not a visceral shudder of revulsion because you know your cousins well, so for anybody to subsequently meet and love a cousin in later life is wrong, wrong, wrong, if the worry is really about the children then rather than driving it underground with ban, ban, ban, it seems to me to be far more sensible and ultimately productive for the children born to such a union to legalise it but make it clear upon marriage that any wanted children should not be conceived prior to genetic counselling and consideration of using a sperm or egg donor (which also brings out the fervent 'well I would but what if in eighteen years time there's a knock on the door'/ what if you meet your brother or sister, ew ew ew') brigade out.
Facts can be racist when only certain facts elicit gasps of horror and shudders of revulsion where other equally unpalatable facts are either ignored or treated sympathetically.