"Innocents" seems to me a generally lousy choice for kids, unless you are
thinking of makinga very small and careful selection of chapters.   And
then maybe junior-high level or older?

Some of the  slapstick-type humor would still work for kids, as in the
chapter where he has always dreamed of a luxuriant Parisian shave....and
then gets his hide nearly ripped off.   And I'm sure a couple of the
encounters with guides would still be very funny.  Like the scene where the
guide expects them to go into ecstasies over a mummy, and the doctor asks,
"Is....is he dead?"

There are also bits of commonsensical humor that ought to work
nicely:  Some of the attacks on tourist idiocies and American chauvinism
abroad, for instance.  Or the scene where most of the pilgrims go into
guidebook-induced ecstasies over the facial "expressions" in an unrestored
masterpiece (DaVinci's Last Supper??) and Twain points out that the fresco
is in such lousy shape that you can't see the expressions.

But the book overall is awfully sprawly.  And the basic humor
mechanism--'this is what the guidebooks say; but, aha!, THIS is what it's
really like'--demands a tolerance for Victorian guidebook prose, values and
stances that seems to me well beyond the patience of most kids.

It seems to me you would have to create your own 'book' out of a judicious
sampling of chapters.

Mark Coburn