Personally, I would opt for the protestant stream.

This is because in my honest opinion, I believe the protestant education would be broader than the catholic stream (because there are many different denominations) and the catholic stream would also include some teachings/rituals/etc which DH and I don't adhere to.

I would not be selecting the non-religious stream because in my experience, a "non-religious" stream/group/class often ends up being an "anti-religious" or atheistic one.

While there may be elements of the protestant teachings which you don't agree with or believe in, they're unlikely to get overly technical at such a young age, and if there are bits and pieces which you wish to teach differently about, I believe it's much easier to explain to your children the differences between parts of beliefs (some people believe that xyz, others believe abc, I believe abc because...) as opposed to them being taught in more absolute terms at school and then having it completely contradicted at home ... (ie: God doesn't exist -v- God does exist, there is life after death -v- there isn't life after death, humans have spirits -v- we don't ... etc).

Not sure whether this helps, but that's what I'd be thinking.