Two year old and sick

My son is 2 and all day been acting off. He has a 101.1 fever. I gave him Tylenol and he’s now sleeping. He ate a little bit today but he’s drinking his normal amount. My 6 month old daughter is also sick but no fever. Both have runny nose’s and a cough. I’m just worried.

What are red flags I should look for so i know when they need to be seen by a doctor/ ER visit?