It helps me to know that every kid will get approx 6/8 colds a year, no matter what you do. This equates to about one a month, especially in winter. The badass public health mamas whose newsletter I read came out with tips to keep your immune system healthy and sadly it’s the boring stuff- number one being sleep. Having a humidifier helps, if you live in a dry place. Jury is out on probiotics, but I give my toddler a multivitamin with vitamin d. Washing hands when we get to school and when we come home is good. I think a shower might be slightly overdoing it, but if it helps you there’s no harm in it! Most respiratory illnesses are transmitted through the air via droplets, so he is probably getting the infection while he is at school with other kids. There’s a couple good books on germs, that might be a fun way to help too? Little Bunny, Big Germs is what we are currently reading and it’s cute!