Do multiple credit cards help or hurt credit score for young person with no credit yet?

I dont think one card vs. two makes a great deal of difference. How you use the cards does. Make sure he understands that credit card interest rates are obscene, and he needs to pay off those balances as fast as possible, preferably by paying the balance in full every month rather than paying the minimum.

I carry two cards so that if one is disabled due to identity theft or other oddities, I can fall back on the other. There may also be some differences in additional benefits like travel insurance, extended warranties, or cash back/points; read the fine print.

Also, remember that there is a huge difference between being offered a credit card application, and actually getting the card. Pre-qualified only means that you met their marketing profile well enough that they think you are a potential customer.

To see what happens, look at the major components of a credit score:

1. Payment History, very major factor. Assuming all bills will be paid on time, no effect.

2. Credit Utilization, major factor. If utilization remains constant on a dollar basis, adding more credit will decrease utilization percentage, which will benefit the score. If utilization increases, this will remain constant or hurt your score.

3. Age of accounts, minor factor. Your average age of accounts will go down initially, hurting your score, but will increase as time goes on. This is the best reason to open accounts now. Banks want to know you've got experience managing credit.

4. Number of accounts, very minor factor. This will of course go up, benefitting you.

5. Credit inquiries, minor factor. Your score will drop for 24 months as a result of the credit pull. One pull should have a minor impact.

Therefore, if used responsibly, a new credit card will give you a major boost, and two minor temporary decreases. As designed, the credit score will drop for a number of months and then recover.

Thus, what one should consider is whether there is a need for opening new credit in the near-term, e.g. home or car loan. If so, then hold off opening a new credit card. If not, then opening a credit card to build history is better done now, to benefit new loans a few years down the road.

Finally, a consideration is that when you're young, try to open accounts that you want to keep, for example at a bank you are likely to stay at. I have cards from college that add decades to the average age of my accounts; I can open new accounts without that factor taking a hit.

Parts of your credit score are likely calculated as a historical average. There are many factors that each credit reporting agency uses, but math can show a comparison of some of the numbers used for a historical average.

Scenario 1:
Don't need a credit card yet and so don't get one, then 5 years later get a CC and your credit record will be 0 years with any financial institutions.

Scenario 2:
Start with one card, 5 years later add a second card. Then your kid needs a credit score for a financial application. Find the average and its half-way between 5 and 0 years. Avg CC age or duration 2.5 years

Scenario 3:
Start with two cards, 5 years later add a third card. Then need a credit report and your average 'historical record' is a higher number. Avg CC age is 3.3 years

(5+5+0) / 3 > (5+0) / 2

Disclaimer: I don't know the algorithms used by the credit reporting agencies. Other factors are included in making the score. Unused cards may affect outcome. Total amount of available credit (debt) may affect outcome too. So more cards may mean a higher available credit amount for what ever that is worth.