Just south of Bellingham you'll find Larrabee State Park. This is quite a popular family/dog friendly park with playground equipment, an amphitheater, and large grassy playing field to let the kiddos stretch their legs. Follow the signs to the beach and you'll find a very short hike under the railroad tracks and down to the sandy beach which is perfect for some summer time splashing. From the beach you can walk in either direction (at low tide) and find tide pools and wildlife all around.
South of the main beach you'll find a trail that follows the coast for a little bit leading right onto large rock outcroppings that get you about as close to the water as you can get without getting wet.
To the north of the main beach is a boat launch located in a semi-protected bay that's perfect for launching your kayaks and paddle boards and get you onto the water.
If you're really adventurous there's some rock-climbing walls located all over the park. Some with anchored sport-climbing routs and many with access to some easy beginner friendly top-roping spots. For more info on the exact spots I'd recommend reaching out to a couple of the local outdoor gear shops located just a few minutes up the road in downtown Bellingham.
If you're after more hiking options the State Park offers itself as a great basecamp to plenty of local hikes just a few minutes away. Oyster Dome is a local favorite and the trailhead is just up the road from the park entrance. Make it to the top of the 3.5 mile scramble up and you'll enjoy a stunning view of the island dotted Puget Sound. Be warned though that hike comes with some sections of quick vertical gain and unapologetic amounts of switchbacks. There is two entrances to the trail, the trail located on Chuckanut is the steeper longer of the two. (the link above has more details on the trail)
For an easier hike you'll notice a trail head just across the street from the State Park main entrance. This trail leads to Fragrance Lake and is a mild 5 mile roundtrip hike into the lake where if you stop and read a couple of the signs along the way has some Native American legend to it. There are plenty of other worthwhile hikes in the area but I'll leave a little room for exploration here. ;)
If all of that hasn't convinced you to make a trip here yet then the drive might just make it worth it. Chuckanut is one of Washingtons most scenic historic roads that creeps between the flat rack cliff faces and the old stone walls of the original highway north. You'll get spectacular views at every crack in the trees. There are 4 or 5 scenic look outs on the road, all of which are worth a few minutes of your time. If you're heading north to visit the park, then take the detour in Burlington and follow the signs to Chuckanut. You won't regret it.
Here's a little video to convince you to check it out for yourself.