Print as many copies as you need. Hand them out, sell the printed copies, put them in a workbook, or open the SVG and change it. No attribution is required and no permission is needed.
The one thing not to do is re-publish the files as a downloadable collection presented as your own, because that is the site rather than the sheets.
Every sheet on this site, the pictorial coloring pages included, is generated from geometry. No third-party artwork is involved anywhere, which is why the permission above can be given without qualification.
Letterforms come from two typefaces used under the SIL Open Font Licence 1.1: Andika by SIL International for print, and Playwrite US Traditional for cursive. Only their outlines are embedded, and the OFL permits that including in commercial work. Neither font is redistributed as a font file.
Holiday dates are computed from the US federal statutory rules rather than copied from a published table.