Psalm 90:16 "May your deeds be shown to your servants, your splendor to their children."
Though we want our kids to be happy, building self-esteem in our kids is not about making them happy. Just as with words of affirmation and gifts, acts of service is about doing what is best for our kids. It is about making sure they know they are loved, not about pleasing them.
Acts of service is a time to model behavior and activities--everything from every day chores and skills to charitable acts as well. We serve our kids ALOT when they are little. As they grow, we train them to do things for themselves. No, this is not easy. Their first attempt is not perfect. As parents (and mentors) we may have to put aside or at least change the expectations we had before kids.
While it is good to build independence in our children--in fact it is absolutely essential to train them early and appropriately!--acts of service can also be given as a special gift. I know my daughter is capable of picking out clothes to wear and brushing her own hair. Yet, sometimes I can make the effort to do these things for her to say, "I love you. You are important to me. I am not so self-absorbed and busy that I can't take time out to do something simple for you once in a while."
Prayer suggestion: Ask God to help you use each of these "love languages" as you communicate with the kids in your life.