Short of doing full airport screening there's not much more they could do. All the recent attacks have been on relatively soft, insecure targets. I'd say DLP is a pretty hard target as detailed by Sugaroo_
Even these despicable people will do there own risk/reward analysis when planning their next attack so given that DLP could well be one of the most secure outdoor spaces in France, they will probably conclude it's probably better to try hit somewhere easier.
I'm not saying anyone should take unnecessary risks, but if you stop taking your family on holiday then these abhorrent people are starting to win. Be cautious, keep an eye on what's around you & if you see anything that doesn't feel right, report it to police or a cast member. Police, Disney or anyone else who's job it is to keep us all safe would far rather have us report things so they can challenge those people behaving "not quite right" than allow one to slip through the net.
I'm also heading to the French Riviera later in the year & while what happened does concern me, until the Government advises against travel, me & my family will still be going.