Condolences on the death in the family, always a tough time.
I'd say it depends on each family. If it were a lower income family where money is tight, it might not be a smart choice to buy suits for children esp since they are going to outgrow it soon. When I was growing up I never needed a suit till I was 20.
At the same time some kids go to many events or out to dinner where a suit would be needed, if that's the case I'd buy them one.
I'd say around 20-21 would be when I would really invest in my kids wardrobe instead of buying them beaters. They've stopped growing, and are entering like 3rd year in college, so they shouldn't be gaining too much more partying weight and are going to start interviews in the near future