Christmas 2: the 4 R's: Galatians 3:26-27 little kid or grown up child of God?

Child of God is Child of God, right? Not so fast. Turns out that adult children have more privileges than young children. What about you?

I'm following the Daily Bread's 10 day devotional for Christmas. If you are using the Daily Bread for your devotions please READ the scriptures they suggest. The Daily Bread's 
devotional material is well written and helpful, but it is NO substitute for the Word of God. If you have to choose, then spend your time reading the suggested Scripture passage and bypass the devotional.

REST: Take a few minutes and quiet your heart before God. Prepare yourself to hear from him. Here are some rain sounds to help you relax. If you live in HK or the Philippines, you can open your window a bit and you'll have a good chance of hearing rain. :-)

READ: Today's reading is Galatians 3:26-27

"For you are all children  of God through faith in Christ Jesus.  And all who have been united with Christ in baptism have put on Christ, like putting on new clothes.    There is no longer Jew or Gentile,  slave or free, male and female. For you are all one in Christ Jesus.  And now that you belong to Christ, you are the true children  of Abraham. You are his heirs, and God’s promise to Abraham belongs to you."  Galatians 3:26-27

In my version there was a footnote icon next to the words "children", so I clicked on it. It said "Greek  'sons'". That means that in the original the writer used the word "sons" instead of "children. So one of my questions is:

• What is the difference between "son" and "child"? 
• "united with Christ in baptism" - What is the role of baptism in my union with Jesus? It sounds like baptism is where I take off the old me and put on Jesus, where I take on my new identity in Christ and become one with other Christians. 
• "true children (sons) of Abraham: What is a true son of Abraham? a false son?
• What does any of this have to do with Christmas? Why did the Daily Bread include this in their Christmas devotional? (not an important question)

There is no way to answer most of these questions without reading around. Read the paragraphs before and after this passage. What if I don't have time? Then slow down, save it for tomorrow. Let the question cook like "long soup". Pray about it off and on during the day and at the next opportunity read around to find the answer.