They can eat them cold or I would just pop in boiling water x
My son just ate his cold/room temp
We started by taking boiling water in a thermos and pouring into a bowl to heat it. My little boy wouldn't eat it cold. Then we tried heating in the microwave first befofe we went out and then pouring into a food thermos to keep it warm. I'd say that method was fine for lunch but probably no longer. As there's not loads of food in the pouch, it went cool quicker than I expected.
Could you heat it up before you go and get 1 of the cups/flasks that’s insulated so keeps it warm? x