The Amish are extremely business savvy, shrewd negotiators, and have no issues being active members in the economy. They also own vast tracts of very valuable land (especially in Lancaster, PA). Combine that with being frugal and austere, and it's a recipe for wealth.

For childcare, their community focus let's them share the burden amongst the larger group. Additionally, children are not nearly as coddled and are expected to contribute to the family's work, and help co-parent their siblings.

Compare this to the average nuclear family: underpaid, barely any savings, most likely rents, and lucky if they have even one family member nearby that can share the childcare burden.