Greetings! We’re headed to the Brac soon and will be staying for two weeks. We have read that for snorkeling from the shore, it is really important to have good foot protection. I bought a pair of Aqua Lung Low Tide Socks w/ grip, which fit nicely into my fins. But, they are only 3 mm. I’m not sure I trust the advice of a MinneSNOWta scuba shop. Will this be protection enough – especially against sea urchins, if necessary? I have yet to find anything small enough for our 8-year-old. Ideas? Many thanks!