Finish for a painted white desk top

Hi, I'm looking for a little advice, I've built a couple of these desks for my kids and both I sprayed with standard oil based paint (2 x undercoats, 2x top coat). Everything has held up well for the last year except for desk top. They've had a fair bit of use but I think all the glue spills and drawings with texta has caught up with the desktop and it's starting to look pretty grubby.

The kids are hading back to school in 2 weeks (woo hoo), so I thought it might be a good time to re-coat.

Any advice or ideas on what to re-coat it with?
Attachment 473506

The least hassle would be recoat with the same paint as before. Perhaps use some clear plastic table mat as protection. I cant think of any coating that is truly child proof.
Regards
John

Thanks John, that might be easiest option.