As others have pointed out, what this comment proposes is wildly different to what Wealthfront and Betterment do. Active trading, algorithmic or otherwise, is unlike buy and hold investing which Betterment and Wealthfront advise. Buy and hold is also simpler. The value-add of a robo-advisor for buy and hold is automating:

A) Keeping a portfolio balanced and

B) Taking advantage of a fairly specific set of tax loopholes in order to make those investments slightly more tax friendly. (where "slight" can become substantial over a 15+ year period of compound interest)

I know that some programmers have written code to automate their Vanguard accounts into something similar to a robo-advisor. This, to me, is much closer to programmers taking an interest in self-built robo than what the parents proposes.

Auto-rebalancing is fairly easy, you setup your account to put deposits and dividends into a money-market account then write a script which moves money from the money-market account into ETFs at the correct ratios. Tax-loss harvesting is slightly more complex but is doable.