"fish paste" means: Any of several varieties of spread, made from physically processed cooked fish with the addition of some cereal, traditionally eaten on toas.... This is a fairly neutral word with no inherent risk attached. There is no real cause for parental concern; it is descriptive vocabulary rather than something dangerous. If your child uses it, context will usually make the meaning clear. A brief, curious question about where they heard it is generally enough to know whether to follow up.