I just wanted to share a couple of photos of my kids wearing their Synapse 19s. They are age 8 and 10, and the bags fit very well when I cinch the straps way down. Both prefer to use the chest clips, but there really isn't much shoulder slippage, even when they skip the clip.
2014-03-07 15.00.23 by agtobler, on Flickr
2014-03-07 15.00.30 by agtobler, on Flickr