The national seashore is really great, and by that I mean the beach. Definitely fit for families, however note that the bathrooms are pit toilets. There are changing stalls as well and a shower for you to rinse off.
Be aware that anyplace in the marsh or wooded areas are ripe with mosquitoes. I've traveled a lot and this would be up there as one of the top mosquito laden areas. There are also ticks, deer flies and horse flies to contend with.
Horses can be seen from the road leading to the beach so try that before donating blood.
Definitely worth the visit. It is $20 per car entering from Chincoteague. More