Simplicity Pattern number 1434, size 10, boy's pajamas. I cannot find a date, but I'm guessing it to be from the 1950s-60s due to the price listed on the front of 45 cents. Pattern has been cut.
Note on the back; "BOY'S PAJAMAS IN TWO LENGTHS: Shown in summer and winter styles these pajamas may have short or long pants. All versions of pants have elastic at the waistline and fly front closing. Short or long sleeved top may have a button front closing with a convertible collar or may be a pullover style with band at neckline. Corded piping details view 1 and 3 tops."
Address for Simplicity Patterns Co., is listed as 200 Madison Avenue, New York 16, NY. Note on the back flap claims "Ask for the Simplicity Pattern Book The Fashion Magazine for Women Who Sew on sale at pattern counters and newsstands."
Darling old pattern.
It still has its instructions, however I don't know sewing well enough to know if the pattern is complete.