"Jewish modest dresser here. Wear skirts out of the house and no sleeveless. having a hard time with DD who goes to a school where all girls where skirts, but on weekends at birthday parties all girls wear yoga pants, etc. she is 7. she was the only girl wearing skirts at a gym party. maybe she should go to a more observant school where the girls wear modest clothing out of school also? it seems so hard to make your child the outsider, even when it's in your own community, supposedly."
Before I sent my girls to a "more observant" school where they have a higher chance of being told that they can't study Torah as adults, shouldn't go to college, are obliged to submit to their husbands in marriage, etc., I'd buy them some long tunics or skorts to wear over yoga pants. Why chance a major problem instead of solving the relatively minor one?
My DD wears yoga pants all the time, often under dresses but sometimes with just shirts, and I have not noticed that it is damaging her natural modesty or her Jewishness. But she is four. By the time she is 7 I will probably not want to see her spread-eagled in yoga pants in public, so I sympathize with your dilemma.
DD owns about five versions of this outfit: http://www.hannaandersson.com/style.asp?from=SC|65|2|24|25|3||&simg=36325_B59, only with ankle-length leggings. With a sweater on top or long-sleeved white shirt underneath, it's very modest and entirely functional and she doesn't stand out at her Reform preschool. Nor does she stand out among the Chabadniks. And really, not standing out as a physical spectacle is kind of the point.