I use anchovy fillets in alot of recipes to add umami and nutrients, not just sauces but also things like meatloaf. Fishiness dissipates pretty quickly with heat, even faster with acidic ingredients like tomatoes, citrus, or vinegar. It's pretty easy to modulate fishiness, even with just acid. I double or triple the anchovies in a typical caesar dressing recipe, and if I feel I over did it just adding more lemon juice tamps it down.

One of my kids is pretty picky, even sensitive to onions, but doesn't seem to pick up on the anchovies. She'll eat fish, though, depending on mood, so maybe she's not the best benchmark.

That's the spirit! But you shouldn't underestimate the power of suggestion:

"This was cooked with fish sauce" -> "This tastes fishy"