In terms of solids, the point that hasn't been made yet is:

It's best to offer the breast first than give the solids because the mom
may have a sensitivity to any food in the baby's mouth that hasn't been
fully swallowed. How many of you have seen sore nipples as a result of
solids first than breastfeeding?

Also, about solids at 4-6 months as WIC guidelines, the reason I see WIC
saying as early as 4 months is because, since WIC is a food supplemental
program, the moms who are not b.f. have to end up buying formula at
their expense. As baby's intake increases, by the 4th month moms are
anxious to introduce solids because of the cost of formula. Also, I
think there is a fear that moms will water down formula or that they
will start solids anyway. Giving the cereal vouchers at 4 months may
help keep the formula fed kids more in line with WIC nutrition
guidelines.

Assunta Osterholt, IBCLC