If you baby sit for your grandchildren, ask to be paid in cash, at the going rate. Sound callous? Read on. You can contribute the earnings — up to $2,000 per year — to a Roth IRA. Here’s the payoff: Name one or more of your grandchildren as beneficiaries of your Roth IRA. Eventually, they’ll inherit. Then they can stretch out the tax-free compounding over their life expectancy, which may be 50 or 60 years.