Could be heat rash, baby acne or insect bites. Check this out:
Rash - child under 2 years: MedlinePlus Medical Encyclopedia
Calamine lotion is safe on baby's skin and works wonders on heat rash in just 2-3 applications :-)
If you've just started baby on solids, you might also want to check if there could be any allergies related to food too. Hope this helps.