According to The QI Book of General Ignorance, "Peanuts, almonds, pistachios, Brazils, cashews, coconuts, horse chestnuts and pine nuts are not nuts. So the legendary health warning on a packet of peanuts ('may contain nuts') is, strictly speaking, untrue."
Allergies are funny things though, and I wouldn't like to say whether or not coconut is safe for your kids to eat (plus the biscuits in question could actually contain traces of real nuts). Suffice to say that the above book tells me that coconut water (you get the milk from boiling it down) is completely sterile, packed with vitamins and minerals and has the same balance of salts as human blood, therefore it makes an excellent hangover cure.
Not that your kids (hopefully) will need that information just yet.