Is it the sheer number of dwarves that's the problem, or children's relative uselessness (ie. you wouldn't mind the excess pathing so much if they earned their keep)? The second can be dealt with by assigning them labours via Dwarf Therapist. If it's the first and you have the dwarfpower to spare, draft a number of useless haulers equal to the number of children and station them under a raised bridge.
Or you can build a childcatcher. For this you need some hatches and some doors attached to a pressure plate over which every dwarf must pass. When an adult passes over the plate, nothing happens. When a child (size 4) passes over the plate, hatches open to cut off the normal pathing and doors open to provide an alternate path. This alternate path takes them over a different pressure plate and then a bridge. This bridge is, naturally, attached to the pressure plate which the child has just triggered. What happens next is up to you. A raising bridge is the most efficient solution, but will result in an accident sooner or later (since an adult on the same tile as the child and the pressure plate will also be forced onto the alternate path). A short* drop into a chamber with a dummy lever marked Pull (R) and preceded by an adult-only pressure plate and a retracting bridge over a shorter drop back into the fortress should return any adults back to wider society.
*2 z-levels is good.