ds had a pair of trainers once with elastic laces and a sort of slider to tighten/loosen them similar to http://www.millets.co.uk/millets.storefront/product/082696.aspx?breadcrumbs=MIL%20SS06%20Kids;MIL%20 SS06%20Kids%20Footwear theseCan you buy these separately ? dd has some lace up canvas boots but can't tie them herself.