How to boost a 4 month olds immune system and overall health

[1love4ever]

A friend of mine has a 4 month old baby who is on forrmula and goes to daycare and is always getting sick.  She also has problems with gas.  I recommended http://www.amazon.com/Garden-Life-Probiotics-Kids-3-4-Ounce/dp/B004H9O4VG/ref=sr_1_3?ie=UTF8&qid=1318124000&sr=8-3 Garden of Life Raw probiotics for kids, they are for 3 month old and older.  She is going to get them, but still would like to know of other options as well.  Does anyone have any other ideas or suggestions?

Thanks

[MommyThea]

On a 4 month old, probiotics were my first though also.  I've never boosted that young...but vit D drops? I'd be worried about allergies and such in that young of an age. 

[1love4ever]

Formula is fortified with more than enough vitamin D. 

[blessedwithboys]

Donor human milk?