Alberto,

My daughter started fishing with me when she was 8 and I started her out on a 9' rod. The extra length to the rod helped her keep the line out of the dirt on the back cast. She can now cast with just about anything but likes my 8'6" rod the most. What I'd be most concerned with is rod weight. A 4-6 weight is generally ideal, but I'd go for the lightest (physical rod weight) rod you can reasonably afford as kids arms tend to wear out quickly due to needing lots of extra casts until they are decent casters. In my case I opted not to buy her anything but just let her use a rod I could "tolerate" her breaking if it came to that.

Brian