Sibling Squabling..

They need time apart to do things with their own friends. Have lots of things for them to do where they don't have to be in the same room. They'll find when they're together they'll like spending time together but it's entirely on how much time they've spent apart.

I usually just separate them. Mine share a room, so one of them can stay and one come to the kitchen or living room. I usually don't get involved. It's rarely worth it to try and figure out who said what or who started it or enter into the drama. Just separate them and help them find something else to do. It usually don't take long before they start happily playing together again or at least getting along.

My oldest two were the QUEENS of bickering - every day, all day, all the time. The one thing I learned is to stay out of it. Unless it gets physical, I simply do not interfere. Bickering is two fold - part one is normal disagreements with each other and part two is how much drama and ruckus can I create by getting mom/dad to intervene (hopefully on my side) into the situation. Once I removed all adult influence from their bickering, it immediately cut in 1/2 (because 1/2 of it was designed to annoy me and cause ruckus). Also, by not interfering, they did learn some problem solving skills on their own. If one/both of them would try to involve me in their insanity, I would simply say "figure it out" and walk away. Did it completely go away. Nope. Did I need earplugs some days? Yep. If the bickering devolved to the point where I did need to step in, both parties were equally punished. I never took sides, even if one kid was more "right" than the other. I will say this - after learning the hard way with my first two, I employed this technique at a much earlier age with the rest of my kids (I have three sets of kids that are very close in age to each other - girl/girl 21 mo apart, boy/girl 4 mo apart, boy/boy 18 mo apart) and my other two "sets" bickered MUCH less right from the get go.

As an aside, if a nanny had to call me at work due to fighting, there would be some very serious consequences when I got home from work for both kids.

Good luck - summer can be tough months for kids who like to argue!

There is no need for them to be together all the time.
They each need some space.
Siblings are not joined at the hip.
Divide and conquer.
When the squabbling starts - they each go to different corners/rooms/floors of the house.
Or better yet - if there are play dates - one can stay home while the other visits a friend - or they both go to different friends houses.
Make sure you have some one on one time with each child.

I can sympathize.

One of mine generally starts it. My moody child..

I don't intervene usually ... unless they just keep nit picking on the others because I don't think kids should have to put up with that. It's like critiquing what they are doing .. like "stop doing that so loudly..." and I'm like "Ok, out you go till you can be decent to people."

My feeling has always been, if they treat people like that in the real world (school, later on at work, etc.) people will drop them as friends, so they have to not be included for a while.

If two or more kids are fighting, then I separate them. Or throw them all outside. It is usually from boredom I find, or we need a friend(s) over to change dynamic, or send them off to friends - or take them all to park or something .. just divide them up.

But for the most part, I let them deal with it. It's taught my younger ones to be toughies (usually the older ones start it).

Siblings squabble.
The nanny should have instructions from you on what to do if it gets out of hand so that she is not calling you at work.
For the most part, my mom ignored squabbling between my sister and me - told us to work it out peacably or take it outside so that we didn't get blood on the furniture.
If it continued and she got tired of hearing it, she would put us in separate rooms (no toys or entertainment in either room) and forbid us to talk to one another or even think about one another until she said we could come out. Of course, within a few minutes, we were begging to be allowed to play together again.

They are going to battle and get in to arguments with each other, it's normal.

My almost 12 year old and 8 year old are almost the same people...girl is older, boy in younger. They are so much alike it's scary. They were at each other the other day when we were doing our normal chores (all which take less than 10-15 minutes if we just do them). They wouldn't stop so they both got one extra chore. That made them stop. The extra punishment chores are ones they dislike....like cleaning the stairs or cloroxing every doorknob in the house. Easy, but not fun.

That and they both get in trouble every time. It doesn't happen too often because we don't put up with it.

When mine fight they lose privileges. I don't care who starts it because it takes two to fight, either can choose to walk away and not engage, so if they are fighting they both get equal punishment (plus they both always claim it is the others fault anyhow). It doesn't stop it, but it lessens it for a time usually.

When my older kids were younger, separation. One in the kitchen, one in their room, and one in the living room. They did not have electronics so they had to have something else keep them busy. Then when they were okay again, I gave them something to do together. When they got really out of hand, they were separated with NOTHING to do. They hated it. They had to just sit there.

For my younger 2, I don't have a way to separate without them bugging someone else. Drives me nuts. But I am at work so dad will have to figure something out.

You got some good advice below for separation and distance.

My first thought was to question your nanny's judgement and abilities. If there wasn't blood, she shouldn't have called you at work.