Arnold's Son?

Can someone explain to me why it took 13 years to figure out this was Arnold's kid?

The baby mother and former housekeeper did an interview with HELLO this week and, after 13 years Maria Shriver asked if Arnold was the father of her son.

Look at this kid. It took 13 years to figure that out! Are you kidding me, they look like identical.

Also,and maybe its just me, but I think even the mother kinda looks like Arnold.