If your country is part of the visa waiver program and you’re coming to the USA any time in the next two years, you’ve got one month to fill in the ESTA form for free before you travel. After September 9th you’ll be charged $14. If you don’t fill the in, you can’t come.
And just as an FYI, do be sure to double-check the current rules for children’s documentation. Good friends of ours were flying from Frankfurt to Miami on their way to Colombia and their middle child’s children’s passport (Kinderpass) was rejected because it was issued after a certain date. His siblings were allowed through because their identical documents were issued before that date. He and his father had to stay home for an extra week and apply for an express passport (Reisepass) so that they could join the family.
This is the case for German documents, but I imagine other countries are affected as well.