When I opened a custodial account for my daughter, I had my heart in the right place, but I didn't put together a great plan for what stocks to buy. Now, nearly three years in, she has a few dozen businesses that I believe make the world a better place for her future -- but I had no specific focus or investing direction.

As we move toward a new year, I thought now was the time to create a new decision-making process and focus on seven "core" stocks to add to each week. I chose seven to match her age, allowing us to add one new business idea that fascinates her each year.

By concentrating on companies that are easy to understand, or ideas that she loves, I hope to help my daughter notice that investable businesses are everywhere.

Today let's look at the three non-dividend-paying stocks among these seven core holdings -- Chipotle Mexican Grill (CMG -0.41%), Boston Omaha (BOC -0.19%), and Idexx Laboratories (IDXX 0.65%) -- and see why I think they're surefire investments for my child's portfolio.

1. Chipotle Mexican Grill

With its cheese quesadillas in a tie with Casey's General Stores' pepperoni pizza for go-to meals when I ask my daughter what sounds good for dinner, it was a no-brainer to add Chipotle to her portfolio. Not only does the company offer understandable operations for her to learn from, but its stock has been firing on all cylinders lately.

Up nearly 400% in the last five years, Chipotle is recovering nicely from the food-safety concerns that plagued it in 2015.

As worrying as these issues were, the company has rebuilt its image of having high-quality ingredients, ranking 45th in Comparably's 2022 list of Top 100 Brands.

Now operating more than 3,000 stores, Chipotle has ambitions to grow to over 7,000 over the long term as it expands across Canada and into smaller cities in the United States. In addition to this store-count growth potential, the company recorded an 8% increase in comparable-restaurant sales in the third quarter compared to last year.

Powered by the opening of 43 new stores and the strong performance from its previous locations, Chipotle grew sales by 14% and earnings per share (EPS) by 28% in the third quarter. Even better for investors, the company's return on invested capital (ROIC) has rapidly improved over the last five years.

CMG Return on Invested Capital (Annual) Chart

CMG Return on Invested Capital (Annual) data by YCharts.

Stocks with a high and rising ROIC have a history of outperforming their peers' share prices. That makes Chipotle's top-50 ROIC ranking among the S&P 500 index look very promising.

However, despite the company's growth prospects and improving ROIC, it has a price-to-free-cash-flow (P/FCF) ratio of 44. Because this is nearly double the median figure of the S&P 500, Chipotle is a great company to slowly add to my daughter's portfolio using dollar-cost averaging, as better prices may come along over time.

2. Boston Omaha

While a billboards-and-broadband company may not sound like the best stock for a young investor, Boston Omaha's Link Media Outdoor billboards are a common sight for my daughter. This presence makes Boston Omaha an attractive core holding, offering an advertising business that's reasonably easy to understand and that she can see almost every day.

Since it operates as a conglomerate, the rest of Boston Omaha's business is far more complex, yet the simplicity of its core segments makes it an outstanding stock to learn about. Moreover, should my daughter grow interested in stocks, the company would be a great example to highlight how businesses can use the money they earn to invest in other companies.

This is precisely what Boston Omaha does with the cash generated from its primary segments, making investments through its Boston Omaha Asset Management unit. Focused on the ultralong term, the company's co-CEOs (one of whom is Warren Buffett's grandnephew) emphasize decentralization, cash generation, and shareholder-aligned incentives for management.

Although Boston Omaha has grown its sales by more than 700% over the last five years, its share price has barely moved:

BOC Chart

BOC data by YCharts.

Ultimately, CEOs who refuse to provide earnings forecasts catch my attention, highlighting a focus on the long term that feels almost contrarian nowadays. Since Boston Omaha is armed with roughly $100 million in cash compared to a market capitalization of less than $800 million, I'm excited to see what cash-creating businesses it scoops up next.

3. Idexx Laboratories

My final no-brainer investment for my daughter's portfolio was Idexx Labs, with its pet healthcare solutions -- an easy pick for a girl who loves dogs and cats of any kind.

Idexx's diagnostics may be technologically complex, but they're conceptually simple to understand. Whether it's checking bloodwork, liver and kidney function, or vector-borne diseases, the company offers veterinarians a solution for almost anything a worried pet owner needs help with.

Having placed nearly 120,000 diagnostic instruments at veterinary offices globally, the company now generates roughly 80% of its annual revenue from recurring sales tied to this large base of installations.

This razor-and-blade model has delivered recurring sales growth of 11% annually since 2010. Riding the strength of these growing revenues, Idexx stock rose 160% over the last five years -- despite dropping nearly 40% in 2022.

After posting three consecutive quarters of declining EPS, the company grew sales by 4% and EPS by 6% in the third quarter, year over year. While its stock traded at over 80 times earnings in 2021, this year's earnings dip was judged harshly by the market.

IDXX PE Ratio Chart

IDXX PE Ratio data by YCharts.

However, 40% of Gen Zers now own a pet under the age of two -- a proportion more than triple that of their Baby Boomer counterparts. This leaves Idexx poised to rebound, with management expecting 15% to 20% EPS growth over the long term as it expands internationally.

While the company still maintains a premium valuation compared to its peers, the pet-parent bond grows stronger with each generation. That makes Idexx a surefire weekly addition to my daughter's portfolio.