Depending on your budget, you have many options from generally least to most expensive:
1. laminate- now come in wonderful colors, easy to maintain, and inexpensive enough you can replace it when the boys are older.
2. Tile, you say you don't want grout lines, but these can be as small as 1/16 inch and matched to your tile for minimum visual impact/maintenance.
3. Concrete- dyed to any color you want. Trendy, low maintenance.
4. Solid surface, Corian for example. Linen is a nice light color with little grains like sand and a matte finish. Easy to care, can get integrated sinks. Can scratch, but scratches might buff out.
5. Caesarstone/Silestone-wears beautifully, but if you don't like the look of the crushed stone mixed with polymers it's not for you. I saw another type in a showroom that had big chunks of stone rather than the small granules, maybe that's more to your liking.
6. granite- lots of beautiful colors to choose from. Very stain and scratch resistant. Very popular, hard to go wrong with this. Most types need to be sealed.
7. marble/limestone, beautiful, but must be careful with cleaning products and even some toiletries. Would not recommend for bath with small boys in general. Subject to scratches and stains. Must be sealed periodically.
Hope this helps!

Corian, limestone can stain and scratch too easy.

STAINLESS STEEL!! lol

I have 1 girl and 3 boys sharing a new bathroom. I put in polished blue marble and so far so good but resealed it after finding out I can't clean it with windex. Currently it looks great but I wipe it down nightly. I don't know if I will be doing that for years to come but right now it is part of my night time routine. I think you can put whatever you want in but I would stay away from honed surfaces for a child's bathroom.

Paddytc

I would be afraid of staining and etching with the limestone. You might also get scratching with the corian or the limestone.

We used blue pearl granite in my son's bath, and it is holding up very well and is a breeze to maintain. Blue pearl is one of the tougher granites and we don't seal it, but it was rather expensive.

For a lower cost little boys bathroom, I would honestly go with something fairly cheap and bulletproof. Cultured marble springs to mind.

Remember, corian can be resurfaced to perfection if you decide you can't live with the scratches. It's pretty impervious to staining, in our experience with our kitchen. There are colors that aren't solid, that would show stains/scratches less, that are still very light. They're mostly shown with kitchens, not with baths, though. The typical-baths colors are plainer, but they are by no means the only colors available.

We don't have a corian sink, though. I've heard that corian sinks can stain when hot colored liquid is poured in...

You might want to stick with a porcelain-surface sink, for the easiest cleaning. You know, in case the boys dye their hair or something :)

We are buying this tempered glass integrated sink/vanity top for our kids' bathroom. Havent got it yet, but I'm thinking it will be easy to clean and hopefully fairly stain-resistant!
Expo has the lowest prices I've seen on it.

Here is a link that might be useful: integrated sink

Thanks everyone. I am stain testing the cameo white corian vs. the blizzard ceasar stone (looked at it again, and the freckles are not so bad really). I am afraid the corian will scratch and read some not so favorable reviews here, so I am leaning towards the cs. Plus it did not do so well on my fingernail polish remover test.

Thanks mayland for the suggestion, but we have already installed porcelain undermount sinks. Just can't see giving my boys marble (after I type this, I am cleaning up the carpet from the sparkly red and green spin-art splatter), and granite is too much movement. Stainless steel? Well,love the look but not so much for the bathroom.
Thanks so much sassyinak for such a comprehensive summary!! It really made me think of all the options.

We've had great luck with both Corian and granite. My sons are the two biggest slobs on earth. They use all kinds of "guy" products--hair gel, shaving cream, after shave, cologne, contact lens solutions, blobby toothpaste, flouride rinse, mouthwash, coca cola, root beer and sprite--all of which somehow manage to spill on their counters. The corian has been there 5 years, the granite almost two. Both counters look as good as the day they were installed.

fatlady-- fyi much to my surprise my marble was cheaper thant the corian that I had picked out. good luck with the clean up. paddytc

We just had this conversatin with the interior designer that we are working with. I have 2 girls and had no idea what to use as a countertop. We are using glass tiles as accents and flooring so I wanted the countertop to be a neutral area. After looking at all the options, we decided to just go with cultured marble. It is really inexpensive, and goes with everything. This is what is in our current track home, and I have never had problem cleaning it. It has never stained, etched, scratched or had any problems. I sealed it once 5 years ago. It still looks as good as it did on the first day. And this is despite my daughters constantly leaving bright pink toothpaste all over the counters on an almost daily basis!

Good Luck