any tips on preventing a newborn from getting a cold?

DH is sick, now DS is sick, and I'm starting to feel sick.

DH is no longer handling the baby but DS is allllllll over her and her toys, kissing her, coughing and sneezing on her.

i feel so bad telling DS to stay away from DD and kissing her but there is no way to stop him from getting into all her stuff and keeping his distance.

any tips on how i can prevent DD from getting sick? she is only 6 weeks old.