I don't think it is a huge deal - but you're saying it's a kids' bathroom and that makes me say don't go with matte. Trust your designer - that's why you hired him/her.

Hello nitaking,

Quartz countertops should wear like iron, better than granite or marble, regardless of the finish as they are stronger on the Moh's scale than just about anything else on the market. Ask your designer for back up information on the maintenance of matte vs. gloss...all of the manufacturers will have it readily available. In the end, however, it's up to you and your designer.....I agree with Mona....that's why you hired them!

Best of luck,
Elizabeth