More challenging than Corgi Pups and Sprinters
It is the 'Magic Tree House' series by Mary Pope Osborne. DS1 read the entire first book on Sunday - about 80 pages - and is begging for the next in the series.
They seem great for improving stamina - DS1 often asks me to read a page or two if he needs a 'rest' but I didn't get a look in with this one.
They seem a little more boy orientated but certainly not unsuitable for girls.
Hope that helps someone