If/ when do allergies become present??

Jené • 23 years old married, mommy to a beautiful daughter 12-22-13 and handsome son 9-8-15.💜💙
My 17 month old daughter has been super stuffy and congested the last few days, I don't have allergies but her daddy does or did. I checked today and the tree pollen was high as for the other two days I'm not sure. Thanks in advance.