How long does separation anxiety last for?

[Pennies]

DD2 (7 mo) goes bonkers whenever I try and hand her to someone else. She's OK if I leave the room and her dad's there (only her dad!) but if I'm in the room she has to be with me, in my arms. It's doing my head in (and my arms, come to think of it!). Does this phase last long?

DS went through the same when he was about 9 months old. It didn't last long, maybe a month. He's 14 months old now and rushes off to join in with everyone and anything he can!

I read somewhere that it's to do with their brains developing sufficiently to know that a person or an object still exists even when they can't see it, so maybe it's a good thing that they go through this (that's what I tried to tell myself at the time anyway!)