The problem with unwritten laws is that you usually don't find out about them until it's too late.

Well-deserved praise for the schoolchildren and young adults of Our Town is forthcoming. They have contributed generously to Children's Hospital each year, often from their own limited resources.

The thousands of letters received during our campaign always include dozens from or written for children. They bear eloquent witness to the big hearts of little (and not so little) people.

I wanted to extend our Christmas greetings to this significant part of the city's population. Bill and I greatly appreciate their efforts. But I had only three letters from schools and youth groups, not enough to tag a column.

It was a good bet that the pipeline would eventually deliver some letters from young people. But I decided not to wait until after Christmas for enough letters to fill a column.

The contributions of the three were reported. Then the "unwritten law" reared its heart-warming head. Letters containing checks from schools, teachers, and related youth or educational organizations and individuals arrived.

The International Year of the Child lasts for just a few more days. The charter of Children's Hospital is valid for another 900 years. Some things are permanent, and deserve our uninterrupted support.

So again, let's give due credit to these groups, and other organizations that help support "the hospital with the built-in deficit."

The guys in Cub Scout Pack 820 in Virginia made a combined donation totaling $12. "The boys decided to do little chores to fulfill the Christmas spirit twice, by giving service to the community and supporting the needs of Children's Hospital."

A school-bus-driving District Liner suggested to her riders on Fairfax School Bus No. 271 that instead of the usual Christmas candy she provided, a collection be taken for Children's Hospital. They enthusiastically agreed, and sent $15 to me for the "free care" fund.

The cafeteria-workers at Kenmoor Elementary School in Landover sent $20 "in lieu of" the present they usually receive from the faculty.

The faculty and staff of Riverdale Hill Elementary School chipped in $25.

Employees of U.S. Office of Education, ESEA Titles IV and V, added $34.

Bilingual members of the French Club of Washington-Lee High School gave $35 raised by a poster sale.

Friends at the M St. branch of American Security Bank decided "with the emphasis being put on children this year" to donate $50 usually spent on intramural gifts and cards.

The officers of the Doswell E. Brook Student Council raised $54.70 by showing two movies and selling refreshments. Another $10 was added by a faculty member to bring their total to $64.70.

Employees of the Education Division of NASA got the interoffice ball rolling with a $65 gift for the hospital.

The all-women firm of Health and Education Resources also sent in a $65 contribution.

The NOAA Committee for Women decided to make donations to Children's Hospital "as a symbol of our interest in the International Year of the Child," and sent a check for $124.

A check for $150 arrived from the folks in the Management Evaluation Branch of the U.S. Office of Education. They raised the money by running a coffee counter and through the non-exchange of Christmas cards.

"The employees of the National Association of Elementary School Principals believe that we, too, are in the business of helping kids," read a letter from that group containing checks totaling $162.

Members of the Honor Society at General Smallwood Middle School in Indian Head, Md., sponsor a penny drive for the hospital every year. The final lines of the student president's letter read, "Never before have we collected over $300. This year we are proud to enclose checks totaling $643.16 to help the children." And I'm thrilled to receive them on their behalf. Keep up the good work, scholars.

The 14 groups mentioned in today's tally brought in a collective contribution of $1,464.86. An additional $2,293.42 arrived in letters from 94 District Liners, bringing today's offerings to $3,758.28.

At the close of business yesterday, we had $61,715.67 on hand. So today's receipts bring the total amount in the shoebox to $65,473.95.

Things don't look too promising for the realization of my pet fantasy concerning our New Year's Eve total. That big old $100,000 mark looms in the near future, but this hurdle won't be crossed in 1979.

See, there I go again. Wishing won't change the dollar totals, but I keep wishing they could because it's clear that we're running a little behind. For those who have forgotten, my address is: Scott Chase, c/o The Washington Post, 1150 15th St., NW Washington, D.C. 20071. I'll be waiting.