Have easels or a roll of paper board on the walls installed for kids to doodle on. Use the washable markers that wipe away easily or Magic markers that won’t stain permanently. As it fills with kids art work, have them framed and placed on the walls through out the office.

How about keeping lots of colorful blocks in your office. Set them up in a place that encourages the kids to build something to leave on display.

hi

what about an aquadoodle mat

there is instant hardening clay, the special markers that only draw on their paper, dry erase boards, color pencils, those furry bendable tube things stickers, paper (cranes and such making) but the best is paint and crayons you could use washable paints however if you are designing the waiting area i would not recommend this.
oh and one last though those magnet drawing pads that have the sand you draw on and such hope this helps good luck

Install chalk boards on the walls, low so that children can reach & play. Another nice idea for kids is to put those distorted fun mirrors on walls too. Kids love those.