I had an CIs interview last year... Info I got was like 800 applications for reception, 500 got interview and 80 or 120 ( don't remember ) got the spots. And of coz u would have a better chance if u r related to top 10 richest in town or some big names .
88 seats for CIS reception. Half of them foreign half of them local (may include local but foreign passport holders). Of course, if u r famous or rich, higher chance to get in. If not wrong about 700-800 applicants but only 88 seats. Have parents interview.
ISF, guess over 1000 applicants and first round only about 500 remains. Second round about 300 remain and last round is parents interview, 180 remains.
Though no guarantee pre schoolers can 100% go straight to primary, I guess they at least train kids in such a way match Primary requirements. Give it a try.