If it's warm enough, a trigger fitting (I got mine from bunnings in the shower isle) on your hose will be good, assuming you're near a tap
). I use one for hosing off sand etc after the beach. As the others have said, a bucket or similar thing will be fine for the 7mth old. Actually if there are laundry facilities, use the sinks in there. They are usually quite big and deep, perfect for bubs to splash in and there's heaps of bench space. That's what I did when my 4yo was little. I used to rinse the sink out with some vinegar first, just to clean it a bit.