I don't have kids, but I think both games are great for kids to learn. The rules are fairly simple and provides kids a place to learn real-life skills. Monopoly was the first game I learned, and I continue to enjoy that game. Kids can learn finance, the importance of seizing an opportunity and learing to negotiate. Please, whatever you do, instruct your kids to not play the Free Parking Jackpot rule. The game explicitly states that Free parking is a just a free resting place and should remain as such. Playing with the jackpot on Free parking just takes away more skillful decision making and places more emphasis on luck, lengthens the game needlessly and ultimately leads most people to not play the game because it causes the game to last longer than it should.
Risk is a little bit more abstract and requires more thinking to truly enjoy the game (although Monopoly requires a lot of strategy as well, it seems that a player can win without more often than in Risk) and as such should be learned a bit later than Monopoly. I love Risk, but I never really got into the game until I was in Jr. High School. My family played both games a lot together, and Monopoly seemed more accessible to me at a young age than Risk. Once I learned Risk though, I never looked back. For me, Monopoly was a necessary steeping stone to Risk. I hope this helps.