I wouldn't let a kid play most of the fremium shovelware. Many of those games are exploitative, Skinner-boxes based games, not that different to slot machines. I can't think those are good for a kid. Not even for many adults.
This can be said about almost all games, so if that is why you should not play shovelware games, then you should not be playing games anyway.
World of warcraft (and just about any other MMO): Kill/do Quest = reward (better gear(money) = Better Kill/better Quest = reward (Better gear/money)
Souls game: Kill = Reward (gear, higher skill, progression, bragging rights etc) = Bigger kill = (gear, higher skill, progression, bragging rights etc)
City builder: Small Well functioning city = Reward (More money, Nice city) = Bigger City = Reward (more money, bigger city/bragging rights) = Even bigger city. etc. etc
RPG's: Kill/do Quest = Reward (gear, level, money, skill and story progression) = more quest's/better kill's = Reward (gear, level, money, skill and story progression)
FPS: Kill = Reward (higher rank, new gear/weapons, higher skill, higher ranking, story progression)
And it goes on and on, but why is this a bad thing? Being rewarded for effort is a good thing, and shovelware games do teach skills like
- Time managment
- Value of working with friends (faster progression)
- That not all rewards are instant (unless you pay for them)
There are probably others, but I don't enjoy games like farmville and the like so I don't know. And I do not know what kind of skill is required (if any) but most videogame skill's are not transferable to the real world anyway, except the social skill's (or lack thereof sometimes)
Edit: There is a talk on TED on why World of Warcraft is the most addictive box opening simulator, and how you can use stats from WOW in order to see what kind of reward percentages are ideal in order to get someone to repeat the previous behaviour.