Best child lunch box for keeping food warm

[Ahahahstop]

My son isn't a fan of sandwiches and I'm looking for recommendations for thermal lunch box that will keep food warm for school

Before I discovered the DTs aren't allowed hot food I bought Stanley food flasks.

I bought a thermos food flask for DS during lockdown when the canteen wasn't open and it fot a small portion of pasta or rice or similar but it wasn't very versatile. I could put two slices of frittata in wrapped in foil or a couple of sausages with a roll with ketchup on the side. It did the job.