You could visit the Quackjeswater, which is a nature reserve very close to Hellevoetsluis and just across the road from the park where you are staying! Breeding Spoonbill and Little Egret in some of the most unspoilt dunes in the Netherlands (as long as you look away from the port of Rotterdam nearby). Black-necked Grebe breeds in the area too. This is one of the few areas where you need to be a member of a Dutch organisation for the protection of nature to visit, but there are day cards available and you could probably get away with being foreign (it's not locked or anything). I've never been asked for my membership card there!
A really nice areas near Hellevoetsluis is the Prunjepolder between Haamstede and Zierikzee: many, many waders and often other good stuff. The (former) islands in the Southwest of the netherlands all have good areas, but it's hard to pinpoint them without a map! The small harbour of Battenoord can be good for Kentish Plover and Little Tern. It may be a bit late in the year for the Brouwersdam (just south of Hellevoetsluis) to be attractive to birders, but the seaside sluice on the south part of the dam (reachable by a feeder road) usually attracts birders.
If you're so inclined, the only European House Crows are easy to find near the station of Hoek van Holland, but probably Purple Herons and Savi's Warblers are more interesting: Kinderdijk (rightfully a tourist attraction) has them, as has the non-touristy environment of the Zouweboezem (already quite a drive).
It's a bit too far from good forest, but the forest south of Breda is probably within reach. It really occurs in any good wood near that town, but you have to be lucky, of course. Mastbos, Hondsdonk and Putven (near Chaam) are all areas where I've had high rates of success.
Make sure to ask anyone with bins if they know something good is around: most Dutch birders should be able to help you!
