Pop them as Sqad says and then cover with a dressing so nothing rubs on them for a day or two. It is so painful if you don't pop them and he won't be able to walk. I have always popped my blisters.
Sqad, whilst you are about, I fell over in the garden the other morning (at 6.00am and fell over a flower bed and a bamboo cane pierced my leg and broke (the cane not my leg!) I think a bit of it is still in my leg and the hole is quite deep. I've been putting antibiotic ointment on it. Question is will the bit of wood work it's way out or should I go and visit the nurse?
Ta.