Excerpt from Gabriel Gustafsson Oxenstierna's letter to Axel Oxenstierna mentioning that Maria Eleonora has taken Karl Gustav to stay and study with Kristina at court, dated January 18, 1634

Source:

Rikskansleren Axel Oxenstiernas skrifter och brefvexling, senare afdelningen, tredje bandet: Gabriel Gustafsson Oxenstiernas bref 1611-1640, Per Brahes bref 1633-1651, page 321, published by the Royal Scientific Academy of History and Antiquities and P. A. Norstedt and Sons, 1890

https://books.google.com/books?id=-MpAAQAAMAAJ&source=gbs_navlinks_s

The letter excerpt:

... Phaltzgreffuen stedze emellan Nyköpingh och Stegeborgh förreser, uthan tviffuell medh magt under denna elden blåsandes, dermedh sökiandes gratiæ, effter som H. M:tt haffuer och tagit hans sonn i håffuet att studera tillika medh vår unge Dråttningh.

English translation (my own):

... The Count Palatine is always going between Nyköping and Stegeborg, no doubt blowing powerfully on this fire, hoping to find grace, as Her Majesty has also taken his son to court to study together with our young Queen.