i think there are concerns that the bbs may hurt themselves in the walkers when they knock into things and stuff. Some are also worried that vigourous movement when the bbs kick off the walkers may hurt their legs etc.
actually, it's been found that walkers dont't really help bbs to walk earlier. And all my nieces and nephews have managed to walk quite well without the use of walkers.
For me, dont't think i will put my dear daughter in a walker cos I dont't want to have to chase after her in a walker. Am still wondering whether to get her an exersaucer tho, but am worried cos there are reports of bbs getting hurt in exersaucer.