There aren't too many other kids in Dead End in Norvelt—but there are a couple of girl scouts. (Where else do you think they got the cookies?)
Mertie-Jo Kernecky is the closest thing to a love interest Jack has, and that's not saying a whole lot. Her smile is "naturally sweet" and she has the habit of speaking in a soft voice while dropping her head to the side like a "dazed sunflower" (21.4). (Ha! That made us laugh.)
Unfortunately, she's not nearly as sweet as her smile. In fact, she's kind of manipulative and calculating, as we find out when her smile is wiped away with "one lizard lick of the lips" when Jack refuses to buy any of her Girl Scout cookies. Being compared to a reptile? Pretty much always bad. In fact, we can't think of a single instance in which being compared to a lizard would be flattering. (Unless you were talking about limb regeneration, maybe. Now that's cool.)
Anyway, lizard-lips aside (see? not flattering), it's obvious Jack likes Mertie-Jo. He tells us as much, but he also adds that he doesn't like her too much because she most likely wouldn't like him back (10.111). She makes fun of him for being afraid of the skeleton in the car trunk (21.27), so she comes off as a kind of manipulative mean girl.
Betsy Howdi is the only other teenage girl we meet in Dead End in Norvelt. She is also part of the Girl Scout troop, but plays a minor supporting role. Jack describes her as having a "mocking dark-eyed face" (10.110), which doesn't make her sound too nice—but still comes off better than lizard-lips.