I have had plenty of experiences with sea lice in Fiji and while I've never used products like Safe Sea, I have spoken to people who have and still got stung.
I am certainly no sea lice expert, but from a purely scientific perspective, I can't see how these products could work. They seem to work on the principle that having this stuff on your skin stops the sea life from attaching to you. But the process is not that simple.
Sea lice stings are triggered by pressure and this pressure happens when the sea lice get trapped against your body. This is why sea lice stings are usually in places such as under your swimsuit, in your hair, around your snorkel mask, or places where skin rubs against itself (e.g the underarms, groin area etc). Once you swim into a sea lice area (they don't aim for you) and the jellyfish larvae become trapped and under pressure, they sting. It's not like they can sense the ointments and then swim away.
Ironically, many people apply these creams like sunscreen to the places they are less likely to be stung. Rashes that just occur on the legs or arms could be sea lice, but are just as likely (if not more so) to be the result of something else like sand fleas (as mentioned by the pp).
The only sea lice discomfort that I suffer from is the moment when they sting. It's like dozens of teeny tiny electric shocks all at once. Uncomfortable, but not bad enough to worry about. I'm lucky to be one of many people that has no long term effects (rashes etc) from Sea Lice. But in saying that, I have always swum ahead to a sea lice - free patch and pulled my swimsuit from my skin underwater to flush them out.
Panicking and getting straight out the ocean, causes the water to flush from your swimsuit, and your swimsuit to suck against your skin. This is arguably one of the worst things you can do. You are causing extra pressure and there is no way for the larvae to escape. I've also read forums where people have recommended wearing rash shirts not realising that this increases the places the larvae get trapped. Sunburn protection - yes. Sea lice protection - no.
From what I understand, even dead sea llice can still sting, so if you do get stung, wash out your swimsuit afterwards.
If nothing else, don't loose any sleep over them. As long as your not allergic to them, I really don't think they're as bad as many websites make out
Hello,
So definitely talk to your kids about them, just so they know what it is if they feel a little sting. I'm sure you know best how to approach it with your kids so they don't feel scared. 
