Unless you want to constantly replace parts, I wouldnt go with a B4 or anything totally race level. Despite what some will say the B4 I have breaks so much that I dont even take it out of its box anymore, and no its not the driving skill, the car's materials are just not up to par. Ive had better luck with my Losi XXX-CR which surprisingly has only broken 1 plastic ball end on the front camber link.
If I were you I would most certainly go tamiya Gator or rising storm whichever you prefer. Its a good way to get back in without breaking your wallet and those buggies are tough enough for your son to eventually take it and have fun with it and withstand some abuse. Traxxas cars are garbage dont even bother...nuff said on that one. Although the slash is tough the materials are so...eh...ghetto

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Tamiya plastic is awesome and unparalleled in terms of durabilty/quality. Go with the gator or the MS dt02 and who cares if its not "race spec". Upgrade parts are available on ebay and are plentiful. So you can enjoy building/upgrading on the cheap without having to worry about constant maintenance. Ive seen races on youtube with DT02's, they do look a bit off on a race track but looks like a buttload of fun!