Some sources on her godparents:
The Digest of the Kingdom of the Netherlands, issue 2, p. 16 (1963) has "Her godparents were the Grand Duchess Charlotte of Luxembourg, King Gustaf Adolf of Sweden, Sir Winston Churchill, and Mrs D. Post-Salomons, the widow of Johannes Post, who was shot as a member of the Resistance on 16 July, 1944, and A. Wiltens"; a 1967 issue of the same publication gives the last individual more fully as "Mr. A. J. Andree Wiltens, a prominent figure in the student resistance movement".
The Illustrated London News vol. 211, p. 427 (1947) gives: "The christening of Princess Marijke, the youngest daughter of Princess Juliana and Prince Bernhard of the Netherlands, took place on October 9. Mrs. Soames deputised for her father, Mr. Churchill, who is a godfather"
Whatever the truth of the matter, Churchill was definitely at least mentioned amongst the godparents, it seems- I don't profess to have any in-depth knowledge of this matter, of course, merely presenting available information.