Depending on the marker, probably will bleed eventually. Best bet is to spot prime with a latex stain blocking primer (all major brands have one or more) then top coat.

To clean, try the Scotch brand equivalent of the Magic Eraser. I had luck with that when the Magic Eraser wouldn't work. Also try to clean the spot with diaper wet wipes. Sometimes that works.

Xylene is in the paint section and will remove even permanent marker.

Hey Andalee,
I know you don't wanna hear this...but I'd strongly recommend you prime that wall after lightly washing it all!!!
* If you only spot-prime, there's a decent chance these areas will "flash" differently than the majority of the wall.
* In your case, I'd use Zinssers' BIN primer. Smelly yes, but the best product for the best result! Keep a couple windows open. The smell is short-lived until the alcohol evaporates, leaving a white-pigmented shellac primer-layer.
* Latex paints are just fine over this. Please use 2 full coats of paint though! You'll need all the durability you can get!!

Faron

Brickeyee is right about Xylene, but it's pretty toxic - check out it's MSDS and use with good ventilation. I have found alcholol to be just as effective so try that first. And yes, Faron is right, prime the whole wall after.

And for the little artist - maybe blackboard paint or an art easel? Definitely encourage creativity, it's an important life skill.

Sky

Sky is right about alcohol. Isopropyl alcohol will get marker, even permanent off most things, not all though. (We have black Sharpie lines in our kitchen grout) We too have a little artist, she is two. We painted our entire house in Satin because of the durability but found that it isn't as durable and scrubbable as we would like. We are actually painting our kitchen and living room with Benjamin Moore's Aura paint. It is very expensive but everything I have read it seems to be worth it with a two year old :)

"but it's pretty toxic"

Not really.
The MSDS is referenced to occupational exposure, not limited 'one time' exposure.

Well, we've got it painted, and it's looking pretty good.

We used Glidden Evermore, and I must say I was disappointed. We used Behr something-or-other (the stuff Home Depot sells) in Satin in the other bedroom, and had much better results. The Glidden was much more watery, seeped under the painstaking masking job, and took a lot more paint (and touchups!). And, to top it all off, this low-voc/low-odor paint still smells after two weeks, whereas the Behr was fine after about four days. (And that's to my highly sensitive pregnancy nose.)

So, thanks so much for all of your advice and help--I'm thinking I was worried more than I should have been, though. DH went ahead and spot covered the marker places (with the white semi-gloss for the trim, ack!) and painted before I knew what he was doing, and it looks just fine. No marker seep through, and no flashing, so I'm hoping we're good to go. (I got 95% of it off, too.)

Thanks again!

Andalee...so glad you got your paint job done! And just had to chime in here about Glidden. My dad told me years ago never to use it, so I took his word UNTIL a couple of mos ago. I needed some trim paint for my kitchen- so little, I didn't want to run out and buy any. So I borrowed some from my son-in-law, and it was Glidden. I went ahead and used it, and it looks fine, but you're right, it was tough going! So from now on, I will stick to my Dutch Boy semi-gloss! (For my walls, I use Behr or BM and even tried ACE recently with good results)!