I've had a couple of sets of very early Milton Bradley Froebel kindergarten blocks in the shop, but this is the first set I've found with a J.L Hammett Boston label, which makes them even rarer.  The J.L Hammett  company was formed in 1863 by John Hammett, credited with inventing the chalkboard eraser, as well as "slating paint" that extended the life of classroom slates. In 1890, Hammett sold the company to a group of Massachusetts investors, and in 1891 partnered with game-maker Milton Bradley of Springfield to produce the first kindergarten materials in the United States. I would date these blocks to the very earliest of those.  I love the lapis blue of the label, and inside is the complete "Gift 4" set of eight blocks, each measure 2" x 1" x 1/2".

About Frobel blocks (There is a terrific website dedicated entirely to to Froebel Gifts - www.froebelblocks.com--from which I've lifted the following text below, written by Scott Boltman.) When Friedrich Froebel established the first system for educating young children, he created a series of playthings to provide children with focussed educational experiences. Up until that time, toys were intended for amusement and education was provided through books and instruction. Froebel's Kindergarten used play as its engine and his Spielgaben ("play gifts") were the fuel. During his lifetime he codified the series of Froebel Gifts up through Gift 6. After his death in 1852, his followers extended the series of educational toys by numbering other materials used in his school.