I had this theory of how the koopalings(including Bowser Jr) came about:
First of all, there are three types of Koopas: koopas(including koopa troopas and paratroopas and hammer bros), magikoopas, and spiked koopas(namely Bowser). So Bowser's parents died when he was a baby, leaving Kamek to raise him. Bowser isn't what I would call evil, but he's in a separate kingdom, and waging war is even more common in our world than theirs, so who are we to call him evil?
Anyway, Bowser marries a spiked koopa lady, possible with blue hair to explain most of the koopalings' blue hair.When the koopalings first starred in SMB3 and then SMW, Bowser's wife was upset about her children being used in military units, and at such a young age, too! So she left Bowser(not a divorce, but she just needed time alone) and Bowser was awfully sorry and hurt that she ran off. Then, less than a year but more than nine months later, he read in the newspaper or some other source that his wife was in a hospital in Isle Delfino and he ditched Kamek and all his war plans and took off to her. Sadly, he couldn't take the koopalings. When he got to the hospital and found her, she was was lying in a bed, and was very, very sick. He stood on the side of the bed, looked at her with care and sadness in his eyes and asked if she would be okay. She wouldn't be okay, but just before the accident/disease happened, she had given birth to another child, Bowser Jr. It was THEIR child, not some other koopa, okay? Since she was on her deathbed, Bowser was sorry that the Koopalings couldn't have come along, but what do you know, Kamek had a change in heart, ditched his own plans from the koopalings, and had brought them with him to the hospital. After the reunion, Kamek took the kids back to the kingdom so Bowser and his wife could have some time alone. Bowser apologized for giving in to Kamek's ideas of using the children for war, and they made up and all that. Then his wife died. After a few years, Bowser Jr. wanted to know who is mother was. Bowser didn't know how to tell him that his mother had died and sort of made up this story about the first woman that popped into his head: Peach. Having to go along with his dumb lie, he ended up going through all the events in Super Mario Sunshine. After all, Bowser Jr. was born there, that's why he sounds kind of like a pianta. After that scenario, Bowser told Jr. the truth, and he took all eight of his kids to the mothers grave, where they left flowers and everyone was finally happy, or at least at peace.
Also, Bowser had no attraction to Peach, she was only used as a captive in war to take over her land. I'm sorry if this was all confusing, but I'm rushing.
“You never really understand a person until you consider things from his point of view.†-Atticus Finch
