Short and sweet should be your bywords, and I recommend you try this even if off-to-school means off-to-college.
- Touch your child; on the head or on the shoulder is good.
- Say a single sentence: "God watch over _____________ while we are apart. Amen." You can make up your own but short and memorable is the key.
- Give them a kiss and send them on their way.
- Repeat tomorrow, after Thanksgiving break, or when they leave to sleep over at a friend's house on Saturday night. Make it like saying goodnight or goodbye. Natural. Predictable.
- Wait for the day they decide to bless you when you leave.
Rituals are powerful for children and adults. They improve the quality of our relationships by giving us common memory and a means for expressing our feelings when the words won't come. They can be internalized, and pulled out when needed. A ritual blessing like this pulls God in as a partner.
Though you may baptize your child with tears as she leaves, you can also bless her with confidence that all will be well. It is almost certain to be - and if it isn't, you will both be aware that God is there too.
In the meantime, I pray that God will watch over you as you send your child off to school.