DC had similar symptoms turned into infection (couldn’t stop coughing with other cold symptoms) in a few days.

If it spikes high tonight - 103ish high, then I would suspect Roseola. It sometimes dips during the day .

is is OP. Well, she has occasional coughing & runny nose for a few days.

Since that 1 hour of 100 degree with red cheeks, her temperature has been fine and energetic. We keep her at home because I thought it might come back. Her temp has been around 99.3 & 99.4 throughout the day, I wonder if it will spike at nightime.

Sometimes my kids are hot on wake-up but not usually an hour after? I wouldn't consider 100 a real fever unless the child is also acting sick. If it comes back regularly I might put her in lighter clothes for sleeping and/or talk to the pediatrician about it. If it doesn't come back I'd just chalk it up to her immune system doing it's job and move on.

Any other symptoms? FWIW, our pediatrician says a fever is a fever at 100.4. He also says "low-grade fever" is not really a thing.

Yestersay night was fine, but waking up with red cheek of 100 degree today morning (upon wakeup & one hr after) . With no medication, and I notice that her red cheek is gone & more energetic and test 98 degree (no fever now).

Okay, did she have fever or not? She seems completely normal now. She goes to daycare (not yoday), and I notice some kids coughing & teacher sudddenly wear masks.