are they 'baby' onion as in meant to be small onions or are they 'baby' as in the size of the plants now - either way I would be tempted to trim the tops off a bit (they've probably been growing somewhere too warm) so that they put some energy into bulbs - don't plant too deeply, just covering the base as you'll presumably be planting them again when they are bigger? If they have been grown on too warm make sure you don't subject them to a drastic change in temperature, do it gradually.