But little kids don't practice/play baseball during the times that they're also playing/practicing football. It's a seasonal thing. And, at the point that it becomes a not-seasonal thing (i.e., if the kid gets involved in year-round travel teams in some sport), the other sports fall by the wayside. So I don't think your analogy holds here.
...he said airily
The ultimate equalizer is the 24 hours that we have in a day. No one has more, no matter how wealthy or privileged, talented or fortunate. The best resource allocation and time management skills in the world will not give you more than 24 hours; it's an absolute hard limit, and you can only tweak your schedule up to a point. At that point, you simply have to choose.
A lot of kids, and even adults play more than one sport at the same time - I don't think that I've ever heard coaches worry much about one sport confusing another.
Even if you do it by seasons - I think the same reasoning holds. Why doesn't playing football in one season and hockey in another mess you up for baseball in the summer? Why don't all those different ways of using your body interfere with each other?
The interference argument one of those things that teachers often say (IMO, to convince people not to wander off to other styles that they might like better, more often than not), but for which there is very little real evidence, and a great many counter examples in modern sports.
I agree - time is the limiting factor, but if that's the case then why not say so instead of trying to make it about one type of training interfering with another (which is how it usually goes) ?