In my opinion there is little that can entertain a toddler quite like water play. I have never met a toddler who doesn't love to splash and pour and scoop.
I look after the children at our churches Mum's bible study. Every Tuesday morning in school term I keep two toddlers and 3 preschoolers entertained so that their mums can meet together and study God's word.
Today I was in the back yard with two screaming toddlers (they do love me - they just don't love me in the moments after their Mums have disappeared). The sand pit had no real effect so I pulled out a tub and the hose and filled it up. We had about an hour of fun with a shovel, two ice cream containers and a water can. We all ended up soaking wet, but also laughing hysterically. Next time I'm pulling the water out first.