Four small things that make a printed sheet much nicer to colour.
160gsm cardstock stops markers bleeding through. Plain copier paper is fine for pencils and crayons.
Turn off 'fit to page' and 'shrink oversized pages' so the outlines stay thick and easy to stay inside.
The sheets are pure line art, so greyscale printing saves colour ink and gives sharper lines.
Laminate a sheet and use dry-wipe markers — the same drawing can be coloured again and again.