The GWS Zero is not a good first airplane for an 8 and an 11 year old. Heck, people with flying experience (GWS Tiger Moth) have trouble flying it...

Ailerons are not that crucial. A properly designed rudder-only plane will turn just as well as an aileron plane. The only thing you can't do is an axial roll, but you aren't going to be doing that with a GWS park flier anyway. Transitioning from a rudder to ailerons should be a non-issue, provided they know how to fly properly.

I would recommend the GWS Tiger Moth or if you want something larger, the GWS Slow Stick. The jury's out on the E-Starter as a first plane (I own one, but haven't flown it, and haven't given newbies the opportunity to fly it). An experienced pilot with a buddy box might make the E-Starter workable (my intention), but your kids can fly a Tiger Moth or Slow Stick on their own.