Stranger Anxiety

I thought my two girls have long ago overcome this fear. No until recently I realised they are actually not ready yet. How I notice this is when I try to detach my girls from my current maid to let my brother in-law's maid to carry them, immediately they burst into tears and cling to us like a koala. As we will be sending our current maid home once the new maid come, I thought to let them mix more with other people so when our old maid is not around they dont find something amiss. When my brother in-law's maid trying to make 2nd attempt to get near them while they are playing, their sense signal enemy, they rather abandon the toys and dash to us : (
I start to sense trouble... even my friends come they also refuse to let them get near. When they meet people outside, they will build up their defence wall, holding very tightly to us. Anytime any people trying to touch them or get near them, they are prepared to scream! I am quite worry when the new maid come, how is she going to cope with this two stress up children? : (
I thought we didnt bring them out too often? When I browse my photo album, indeed about once a month an outing and the itineary of the outing didnt associate much interaction!
Now whenever we meet people in the lift or on the road, we will encourage them to interact hoping can improve their anxiety with people...