It depends on how old your kid is to be honest. At younger ages (u9-u14) futsal is an excellent skill builder. It allows the players to get a lot of touches in a short period of time and because the game is fast paced and there are no walls to keep the ball in like indoor soccer, it forces them to think quickly, have good ball control, and make decisions quickly on the ball. All great for building confident players on the ball which is a necessity in the modern game. The kids are smaller when they are younger and because of this the court feels much bigger to them and they have more room to operate. As the kids get bigger and older, the game becomes very different. Much more tactics are involved and physicality also becomes a factor. It is a hard court and injury risk at older ages increases dramatically. Younger ages, futsal is still much like small sided soccer. At older ages it is pure futsal and a fundamentally different game. Some futsal skills are transferrable to the field but definitely not all. It is a sole of the foot dominant sport and soccer just isn't that.

There are no futsal scholarships or pro teams with real money in the US so the futsal ceiling is very low if you were to progress in the sport. But like said above, great at younger ages for skill building and honing confidence with the ball. Diminishing returns as the kids get older.

Futsal season is already well underway

You probably shouldn't "make" your kids do anything sports related.

Should my kids do futsal or should i just make them brave the cold?