M.W.
I used 'stikins' labels sold here: http://www.labellighthouse.com/
They come in three sizes and have worked well on almost all of my daughter's clothes--even the ones with tagless labels (I just used the smaller ones). I put them in her shoes, on a sippy cup (it's been through the dishwasher a dozen times and the label is still on and reads like it was still brand new), on a few of her diaper bag supplies. Overall very happy with the product.