They're not just in the finish and will not sand out. Neither will they affect the bows performance. I have never found them to affect longevity, but,of course, it would be better it they weren't there. I've always thought of latitudinal cracks as stress from shooting and these longitudinal cracks as "drying cracks". Whatever, they seem to show up in certain models of bows from many makers in brown and especially black glass from the 50s and 60s.
Super glue will not penetrate these cracks and will make a mess of your limb surface, requiring total refinish. Locktite 420 will penetrate about any crack, but is thinner than water and will also require sanding and refinish.
I'd simply wax it real good and take the kid shooting!