Answer: The Rema (OC 263:1) quotes the Maharil (Shabbos 1) who writes that if a woman forgot to light Shabbos candles one week, she should light an extra candle from then on. The Mishna Berura (263:7) explains that this acts as a kenas (fine) to deter people from forgetting. R’ Shmuel Wosner (Shevet Halevi 5:33) adds that this applies even nowadays when there are also electric lights on in the house.
Many have the minhag to light an extra candle for each child born. R’ Yisrael Chaim Friedman (Likkutei Mahariach, Hisnahagus Erev Shabbos) explains that this is in keeping with the Gemara (Shabbos 23b) that writes that one who lights Shabbos candles properly is rewarded with children who are talmidei chachamim (Torah scholars). R’ Menashe Klein (Mishne Halachos 7:35) explains that this is akin to chanuka when one should (according to Rambam) light a candle for everybody in their house (See Shemiras Shabbos Kehilchasa 43:n51).
The Pri Megadim (Eshel Avraham 263:3) writes that if one lit one less candle than they usually do they still need to light an extra one in future. The Mishna Berura (Biur Halacha 263:2), however, disagrees, arguing that the halacha is that one only needs to light one light whereas extra candles is a minhag.
In conclusion, one who accidentally lit too few candles one week does not need to light any extra candles after that.