I do about a cup of plain greek yogurt, a handful of frozen berries, and a glug of milk or juice. If I do chia seeds I use no more than 1T. The chia seeds will make it very thick especially if it sits for a while, if you kid is a slow drinker like mine is. If that's the case I up the juice and lessen the chia.
Other things I've thrown in:
avocado...makes it very creamy and smooth but doesn't impart a flavor
peanut butter...sometimes my kids like a pb&j flavor, or instead of berries I throw in a banana and pb.
Mom to two amazing DDs ('07 & '09) and a fur baby.
Gluten free since Nov '11 after non-celiac gluten sensitive diagnosis. Have had great improvement or total elimination of: migraines, bloating/distention, heartburn, cystic acne, canker sores, bleeding gums, eczema on elbows, dry skin and scalp, muscle cramps, PMS, hair loss, heart palpitations, fatigue. I'm amazed.