I've been to many sedarim with little kids, and until recently, i was counted among them. :) I'll share some of my experiences, both the hits and flops.
Top tip: Get the kids involved. Give them some suggestions - let them pick out which they want to do.
A skit/play/show/whatever-you-want-to-call-it is a classic. Suggested topics include slavery, the plagues, the exodus itself, or (often) all together.
This can be successful, but it has to be done properly. A short one is best. Last year i really overdid it, and nobody was really interested. Keep it in the 5-10 minute range.
The best time for this is Shulchan Orech. This way, the adults can eat while they watch the play. The kids will often be (nearly) full from the matzah, maror, koreich, egg, and kneidlach, so this is a good way to keep them occupied for the rest of the meal.
Maggid might sound like a good idea (we are discussing it), but it isn't, unless you want your seder lasting until dawn...
Afikoman Treasure Hunt
Yes, you read that right! Instead of plain old hide-and-seek for the afikoman, let's spice it up a little. I came up with the idea last year, and it went over extremely well.
It's pretty simple to do. Just come up with some clues leading to locations around the house. At the last one, hide the afikoman. I added a bit of an extra dimension by having all of the clues together add up to one final clue.
There are numerous songs and poems written for the seder. The Dr. Seuss Four Questions is an old favorite. So is Don't Sit on the Afikoman. We've tried a bunch of the ones from this page; most of them are cute once, but not lasting for year after year.
Divrei Torah + Questions
The above things are good for making the seder fun and interesting. In terms of prompting more spontaneous questions, some quick divrei Torah can be good, ideally things that are likely to prompt questions.
Also, have the adults ask questions. Kids can sometimes be afraid of it being a "stupid question". The best way to overcome this is to show that you're not afraid to ask questions.
If the kids are old enough to read and understand the haggadah, i recommend you let them. :) A common custom is to go around the table having everyone read a section. Include the kids in this as well! It might go a little slower, but practice makes perfect, and it's certainly rewarding for the child to succeed in it. And as a bonus, they may come up with more questions from this. I know i have.
Get the kids involved, not shunted to the side. It'll make the seder take longer, yes. It will also make the seder more interesting for everyone.
If you use some of my ideas, feel free to leave a comment saying how it worked for you.