We will need a little bit more information to be able to properly answer your question.
I'm assuming that these blocks were originally intended for printing patterns or designs on fabric. Do you have any indication of their age or perhaps where they came from? Is the pattern/design relatively commonplace - for instance something like leaves or flowers - or would you say they were in a more individual style, perhaps some sort of abstract design? Basically, the more generic the designs, the less likely that they will be subject to copyright as artistic works. And the reason for trying to guess their age is to work out, if they are/were subject to copyright, whether they are still in copyright today or if, because of their age, it can be assumed any copyright has now ended. Since I assume we will probably never know the name of the artist responsible for producing the designs, they would need to be at least 70 years old in order to be reasonably sure copyright no longer exists (see section 12(3) of the Copyright Designs and Patents Act 1988).
If it can be established that the design on the blocks is out of copyright, then using the blocks themselves to print on fabric would be perfectly legal.
On that basis, I don't think there will be any problems using the blocks to print up your own fabric.