Children tend to get anxious when new situations are presented and something that worked for my kids was reading books about blended families. We've gone through many and these are our favorite books for kids about blended families. Hope some of these can help your kids too!!
Growing Into a Family: A Kid's Guide To Living In a Blended Family by Cynthia Geisen
Do You Sing Twinkle? by Sandra Levins
Jessica's Two Families by Lynne Hugo
My Super Stepmom by Nicole Bauer
I threw this last one in here because it's important for children to realize that step-mothers are not the horrible creatures depicted in movies. Step-mothers can be a caring, loving, supportive extra parent that kids need during the transition into a blended family!