Baby yukkuris have very bad fuel efficiency--if you leave them for more than two hours without a feeding, they will die. If you think that's impossible for you, I recommend that you squash your baby yukkuri right away.
Next, I will explain their genitalia (the penipeni and mamumamu). Yukkuris are said to be hermaphrodites, and usually, their genitals appear to be a mere hole (commonly called the mamumamu.) However, if you gently hold the yukkuri and shake her up and down, she will go into heat like this. At this time, the hole swells up and becomes the penipeni.