go down to a garden centre and buy a large spray pump unit it comes with the spray hose, fill it up with warm water pump the unit up, then you have one instant shower.
Have a look on ebay or do a search on google for solar camping showers. Its a plastic bag that holds water, heats up inb the sun and has a spinkler outlet.You hang them up and shower underneath. They are now used by the British Army when in the warmer climes and are great !!!
Now some of these could be good for showering the kids - leaving me to have my shower in peace (they're too young to go by themselves). Will be looking into the various options for the summer.
My mum and dad have larget toilet tent - they hang a shower curtain up round the walls to protect the canvas, and have a small childs paddling pool as a shower tray. For the shower itself, as Jan P suggested, they use a submersible pump with a shower hose and head fitted, in a bucket of warm water - apparantly you can get a reasonable shower from a bucketful as long as you don't wallow!!! They steward a C&CC THS for 4 weeks each summer, the site has no facilites, and this set-up serves them well enough.
I read about someone using a garden pump pressure sprayer, filled with warm water and with a hanging basket lance on the end top ceate a shower. They used it in a toilet tent and stood on a folding plastic crate for water drainage - sounded pretty good to me - just got to be careful about the water run off.
'Hozelock' type spray bottle - boil kettle for hot water & add cold to suit. Pump up the bottle to supply the pressure. Used in toilet tent (we use ours in porch area of huge khyam) and stand on one of those wooden slatted bath boards. Make lots of holes in soil underneath (by hammering in tent pegs) to provide soak-away.
We have an aqua roll with a 240v fish tank heater. The heater takes about 2hrs to heat the water. Once heated we use a 12v water pump connected to a shower head. The shower head hangs up in the toilet tent and the 12v pump is connected to a water proof off/on, whale tap/switch. As long as the site has EHU the system works fine.