The most important thing is to help the kids stay motivated. This happens if they have little successes. Now is the question: What is a succes to a 10 years old? Is it number printed out in command line or is it something colorful, maybe in a web browser? Personally I wouldn't recommend things like C, Assembler - the need month to leave the command line. My recommendation would be HTM/CSS - for a 10 years old this like programming - and then moving Javascript (obvious for the browser) or Python (Pygame and other fun stuff).

Remember, the most important ingredient to learning something is fun. If you got you kid started and it like what it is doing, it will choose the right programming language on it's own.