We've gone through several variations of one of them preferring one of us for a period
of time. I think it is completely normal. I think extreme separation anxiety, i.e. if you leave for a short period of time and the child is inconsolable in your absence, may merit more attention, though. I am sure it depends on the child, but I've always found with my children that if I tell them I'm going out, and when I'll be back (I've even given them clocks, timers etc.