This all depends on what you see the point of ECNL being. ECNL will tell you that they put the best teams/players together with the goal of showcasing the players for college scouts.
My kid has been with an ECNL team since the first year they introduced U13 (7th graders), which is/was purely a cash grab. It may have made sense under the old way of doing things when schools were (foolishly) verbally committing 8th graders. Nowadays they can't even talk to kids until after 10th grade (U16), so the college angle is null and void. The benefit would be playing against good competition, and more importantly, "securing your spot" for the older ages, since it can be harder to crack an established team's lineup at the older ages. But is it worth all the money and time to do so? That's for each family to decide.
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So you're talking about U12s? Allow me to share some wisdom that I've learned here from the forums and am witnessing in real time myself; BEING A GOOD U12 PLAYER HAS LITTLE TO NO CORRELATION WITH BEING A GOOD U16 PLAYER. Take a look at your team. In 4 years only two or three players from your team will be impact players. 50% will have moved on to lower quality teams or quit the game all together. So sure, enjoy your U-little victories now, but THEY DON'T MEAN JACK.