It's safe as far as no dangerous animals and very few people after the last ferry goes back at 4pm, but the only time we saw a ranger was when he was picking up trash and checking permits at about 9 am. What we really weren't prepared for was that the one little cafe/gift shop on the island closes in time for the employees to go home on the 4 o'clock ferry! It's "charcoal fires only" but they don't sell charcoal on the island, or ice, or a long list of other things you might find at a camp store or even a 7-11 for that matter. There was potable water at the campsite and an outhouse about 30 or 40 yards from our campsite. I think it would depend on how old (and hearty) your kids are because you literally have to pack everything in and I think it was between 1.5 and 2 miles one way based on the signs we passed. I think I just googled "Angel Island" for the basics.