Zeeland is my native soil, so what can I tell you what to do. Domburg is located on the peninsula of Walcheren and is a well-known seaside resort and was once in the second half of the 19th century a famous health centre. Also Mondria(a)n (and Toorop) lived there for a while, things like the sea and light inspired him to become the abstract painter as we know him now.
Temperatures in April are usually between 15ºC and 20ºC, but seawater is still too cold for swimming. But as the coast has a slightly different climate, the beach can be with some sunshine in spring already pleasant. Domburg has also a medieval castle “Westhove” , it’s a Stayokay but it’s free to have a closer look. De Parel in the leasure centre is a swimming paradise for kids.
Zeeland is all year around, but especially during summer a touristic destination, mainly for Dutch and German families looking for some rest and fun at the beach. A lot of campinggrounds have their own entertainment for children, but mostly during holidays and peak season.
1-Things to do for kids:
Mini Mundi, miniature park, amusement park and indoor play area in Middelburg, the province capital.
Het Arsenaal Vlissingen, family park with aquaria and a 65m high watchtower for a view over Walcheren and the Westerschelde estuary.
Reptile zoo Iguana also in Vlissingen, this place is also fun for shipwatching, passing by very close to the coast. With a bit of luck you can see a really large containership.
Not in Zeeland, but near Tilburg is the Efteling a Disneystyle family park with a Fairytale Forest, fun for the whole family and highly recommended.
Deltapark Neeltje Jans, there is a lot of criticism, that this theme park does not offer value for the money, the main reason I never visited it. However there is an exhibition about the Deltaworks what gives a lot of insight about the construcion of the Deltaworks, the barrier and our struggle against the sea in general.
2-Other things to do or see in general:
The Storm Surge Barrier itself ofcourse.
Veere, lovely old porttown 15km east of Domburg, trip with the passenger ferry over the lake.
Zierikzee, as Veere worth to visit with a historic shipmuseum in the old harbour.
Climbing De Lange Jan, the churchtower of the old abbey in Middelburg for a fantastic view over the old city centre and Walcheren, good weather permitted.
Bruges is 100km away from Domburg.
Walcheren is excellent for riding with the bike with it's numerous separate bike-lanes and routes. However the wind can be a challenge.
26th of April will be Kingsday with a lot of activities for kids and there will be “ringrijden” in Middelburg, a tournement with people in traditional clothing, men on horseback trying to stick a lance through a narrow ring.
They are now relocating for the moment the football experience to Roosendaal 70km east of Middelburg