I still enjoy The Hobbit just as much as I ever did. It's also not the only 'children's book' that I can still pick up and enjoy. On a basic level a children's story needs one thing, a cracking plot, and The Hobbit has got that in spades. If it did not have that then I seriously doubt it would still be such a well loved book. It also has the element of danger, something which the Harry Potter books share, which makes it exciting (and it has a dragon too, which any child with a taste for such things will tell you is 'cool') and though the protagonist is a grown up, he is a
little grown up.
I think that children especially do not tend to pick up on the absence of either girls or boys all that much, and so the male-centric world of The Hobbit wouldn't trouble them. It has the adventure traditionally assocaited with boys' tales and the magic traditionally associated with girls' tales but most of all it is a fairy tale and such things are universal; whether or not a child would enjoy it would simply depend upon their taste.
Perhaps getting a class to read it as a fairy tale would tempt them more into appreciating it. Maybe even examine it as a Fairy Tale which lacks a simpering princess or a handsome knight?

Really, in comparison to a lot of other children's fiction, and to many of the fairy tales, the omission of women in The Hobbit is no bad thing. Is it better that they are absent altogether than that they are portrayed solely as either love objects or evil witches (fairy tales), a 'good brick' who brings along the sandwiches or a little brat who scweams and scweams until she's thick (sic...

) (novels). I also wonder whether gender is relevant in a novel about Elves, Hobbits, Dwarves, Wizards, Dragons, Spiders, Bears, Eagles etc but
not human children?
Following on from what davem asks about animals as characters in children's stories and if this has any bearing, the
Rupert The Bear stories (as seen in The Daily Express and the much loved annuals) feature a virtually all-male cast list, all of whom are animals. Interestingly the only girl is Tigerlily, a human Chinese girl, and she does not appear all that often. Despite the fact that the stories remain old-fashioned, to the extent that Podgy Pig wears plus fours, they remain very popular for children in the UK.
I think it may be a question of age rather than gender.