My understanding is that when it comes to stem cells being a possible, safe and reliable treatment for cerebral palsy, things are still very much at the research stage.
In my opinion, a good source of impartial advice about stem cell research is the EuroStemCell website:
They have a page specific to Cerebral Palsy:
Personally, I would be confident that if there are any significant, peer-reviewed future breakthroughs with research EuroStemCell will publish about it.
I hope that is a helpful start.