Du Plessis had returned home to be with his wife, Imari, putting a question mark against his participation in the first of a four-Test series that starts on July 6.
But Thursday saw du Plessis announce the birth of their child by tweeting: "Our biggest blessing yet came in a small package. So very grateful."
Opening batsman Dean Elgar led South Africa in their three-day warm-up match against the second-string England Lions in Worcester which started on Thursday.
If du Plessis does return in time for the first Test, opener Heino Kuhn, who replaced Stephen Cook in the squad, would like be South Africa's lone debutant at Lord's.
South Africa made 58 for one on a first day at Worcester where rain meant only 20 overs' play was possible.
Elgar fell for five, caught behind by Sam Billings off George Garton. Kuhn was 30 not out and Hashim Amla unbeaten on 16.
Before play started, experienced South Africa paceman Vernon Philander was ruled out with the right ankle injury he suffered while playing for English county Sussex two weeks ago.
Nevertheless, a South Africa statement said Philander was making "satisfactory progress".
South Africa team manager Dr Mohammed Moosajee added: "Vernon is in the final stages of his rehab following the injury to his right ankle two weeks ago.
"He is building on to bowl at full pace by the end of the week to prove his availability for selection for the first Test match against England at Lord's next week."
AB de VilliersEngland vs South AfricaEngland vs South Africa 2017Faf du PlessisHashim AmlaSouth Africa
First Published: June 30, 2017, 9:09 AM IST