We are on holiday. DH is letting DD1 (7, able to swim) go into the sea alone "but only up to her waist". He says that he is sitting halfway up the beach with DD2 but that he is watching DD1 all the time. He estimates that he could get to DD1 in 20 seconds. I think that this is too long if a child is in difficulty in the sea, and therefore dangerous. I only want her to go in the sea with an adult. He thinks I am being ridiculous. I'd be really grateful for a sanity check! Thanks in advance.