I have a "plastic welder" which I got off ebay for about $80 USD. Used buy-it-now and it was delivered at my doorstep the next morning (kinda weird fast!).
I get red or blue plastic "wire" to use with it from ebay. About $20.
Basically, the thing is an over-sized soldering iron with a flat wedge shaped foot to melt a groove in the plastic and a hole that the plastic wire goes through, similar to a hot glue gun. It's really easy, but time consuming.
My kid's lt230 had shredded fenders, found a pair of slightly better fenders on ebay for $15 (front and rear) but they were cracked badly, no missing pieces though. Took me about 6 hours to "weld" the fenders, then I painted them flat black with vinyl paint. Sort of frankenstein, but considering it's a kids ride, I didn't want to put the cash into new fenders. Looks okay, cheap to do, and holds up nicely.
If you don't have the cash for fenders or you think you will just crack new fenders, then I'd get the welder, it's worth it.
-mike
85 200x <-- too dangerous
91 YZ 250 <-- must be safer cuz its not banned