If you thought your competitive elaborate artcake-buying days were over once you got through your wedding, think again, my friend.
At least if you're in the Bay Area. Because the children's section on cake artist [really, there's no other word] Shinmin Li's website, I Dream of Cake has at least 20 examples of sculptural birthday, party, and birth announcement cakes on it. And if each of those cakes was seen by an average of 50 kids [come on, if you're gonna spend that much on the cake are you really gonna cut back on the guest list? I don't think so.], who'll all want one, too.
Li can clearly do anything with cake, so you can't get out of it by suggesting the impossible; it'll just spur her on--and cost you a fortune. No, I think the thing to do is to express mild, gentle disappointment at the lack of imagination betrayed by your kids friends' choices: Thomas, Shrek, Miss Piggy, Simba, Elmo and Spiderman.
Say, "Sure honey, you could get a Little Mermaid art cake, OR, you could get [dramatic pause] a conceptual art cake, which appropriates an actual Frosting-in-a-Can and Pudding-in-the-Mix cake with sprinkles on it and recontextualizes it with a self-critical awareness of consumerist culture's colonization of our own image-generating faculties. And if anyone gets smart, just show them this certificate of authenticity that accompanies the work.
Or you could give in and just get an ironically cool cake made in the shape of some banal everyday object. Like a cup of Jamba Juice or a toaster. Hey, how about a tub of Enfamil or a case of Pampers? Either way, send pictures.