Hi, my husband and I are both primary teachers and are gearing up for our 3rd move with our 2 boys (now aged 12 and 10). We've always been very honest with them and talked about WHY we are going. We spend a lot of time sharing country information with them (there are some great websites out there that give you the heads up) and answer their questions as honestly as we can.
We make sure that there are ways in place to help them keep in touch with their UK friends. When they were younger, we sent photos back to their friends of their adventures; now they're older, they'll be using email and Whatsapp to keep connected.
Moving overseas offers children a different perspective on the world and gives them skills that remaining in one place can't do - they learn to empathise, make connections with people quickly, realise that nothing is for ever and also moving around the world shows them that kids are kids, wherever you are.
If it doesn't work out, what have you lost? If it does work out, think what you'll gain. Although there may be a few sticky moments at the start, if you ensure they're settled (join clubs, have friends round), you'll find that they adapt to their new environment much quicker than you will.
Best of luck!