Didn't answer the A, B, C.

A. Learning another language at a young age.
B. Don't have any empirical evidence to back my claims of benefits.
C. The reason my eldest started in immersion was because the cost was the same as daycare, but she learned more than at daycare. If the alternative is babysitting or daycare, the immersion school has to be the better option. As I mentioned, we did not consider our kids gifted (not at that age), so gifted didn't figure into the decision.