My kid keeps getting sick

Hey everyone I need some advise. I have 4 kids, ages 5, 3, 2, and 5 months. Last month in early August we went to church and my 2 year old (who goes into a nursery at church) got sick the next day. He was only sick for a few days ( but he was VERY sick), then a week later my 5 month old became sick (runny nose, cough, fever).

The third week of August my 5 year old became sick. Her teacher texted me saying she woke up crying from nap time and that something was off about her. So later that day after she came home her nose began to run (same with the other two), then she got a full blown fever for a week straight, I had to bring her to the emergency room because I couldn’t break the 104.6 fever at home. She got sick worse than the other two. Then thanks to her stubborn self not blowing her nose it came out her eyes. And let me tell you, it looked like she blew her nose out her eyes. There was so much snot coming out of her eyes that she couldn’t open them (my 5 month old and 2 year old are currently still going through this part) . She finally got better and I sent her back to school on Monday. Now she’s sick again this morning and has to stay home.

How do I get this to stop going around my house? I opened all the windows today, I’ve been cleaning their toys, etc . Helppp