Axis & Allies was most complex game I've played when I was a lot, lot younger...then I kinda stopped playing boardames for really, really long time, and started again just a few years ago.

I tend to stay away from such complex games as 1830, anything with weight above 2.5 on BGG I'll most likely skip...not that I don't want to play some of them (like Twilight Imperium or Tzolk'in), it's just that these days, given that I mostly play with kids, at this age, anything above weight of 2 can already be taxing for them (though they seem to like Isle of Skye, Mission: Red Planet and Tikal for example)....I guess eventually we'll move to heavier stuff, especially since they both gravitate toward thematic stuff, which is usually at 3+ weight.

Have you tried Jamaica with you kids? It's fairly light game, with easy rules, plays quick and looks gorgeous. I tend to suggest it these days to eveyone trying to get their kids into boardgames, since I've seen it succeed on numerous occassions, both with boys and girls.

Since you said your 7 year old likes Carcassonne, have you tried Carcassonne: South Seas? We all love Carcassonne (especially Hunters and Gatherers), but I find that farms tend to be a bit too much for younger kids to comprehend right away. South Seas not only sort of streamlines farms mechanism, but introduces resources instead of points with which you load different ships for points....plus it looks much better on table then original Carcassonne.

Colt Express is something that my kids also like a lot, 3D components make it look really great on table and while it can be a bit chaotic, it's lot of fun.