Just keep telling them how much you love them and that things will get better. My son just started a new school this year, he is 9, it was really hard on him the first week. But now that he is making new friends he is doing better. He still missed his old friends and some times he just cries that he want to move back to our old house but I just keep telling him that things can only get better from here on out.
They are young and will adjust. Thats the great thing about kid. Just keep positive.