Osmosis and relations

I’ve just gotten started filtering different types of data using osmosis, using the various filters, but I can’t figure out how to extract relations and all their children from an osm file. If I try:

osmosis --rx input.osm --tf accept-ways natural=water --tf accept-relations natural=water --used-node --wx output.osm

for example, I get a file with all the ways as I want them, but while the relations exist they don’t have any of the ways or nodes that make them up? Is there a way to include them?