oops i guess we had a communication breakdown

When I invite other English speaking expats and their kids over to play in our wading pool, I know how to say it, they know what I mean. Recently I tried to invite some neighbours over, I thought they got what I meant, and the kids and been over to swim before so I didn't think it would be that complicated. But when they turned up, they didn't get in the pool with our toddler. I found out later they had just had a bath and were not allowed to get wet! Last time they swam at our place it was a holiday, and it was with their mum, but this time their mum was at work.