The rake technique works well on lettuce, spinach, arugula, and other salad greens, too, but I like to thin those by hand when the leaves are large enough to use in the kitchen. Several light thinnings, rather than one heavy one, will provide salad ingredients for several weeks. I often seed salad crops more heavily than necessary to ensure plenty of thinnings. Some root crops also can be thinned by harvesting. Tiny radishes, barely a half-inch in diameter, can be used whole in salads.
Baby turnips the size of a dime steam up in just a few minutes, and the leaves can be left on.
If you want baby turnips, however, be sure to grow a variety intended for that purpose, such as 'Hakurei' from Johnny's Selected Seeds. Standard turnips, such as 'American Purple Top', don't size up until the plants are quite large. They will need to be thinned early, before the roots have formed. The young greens can still be eaten. No matter how delicious those young greens may be, you need to know when the crop has been sufficiently thinned.