I live in Coquitlam, so I can help you with this end of it. Rocky Point Park in Port Moody is lovely. They have a great playground and water park, it's fun to watch the comings and goings from the pier and there is a great ice cream parlour. Also make sure to walk under the overpass to go into the little Port Moody Museum. It's a gem, and small enough that you can get around it before your little guy looses interest.

The big public swimming pool (called CCAC for Coquitlam Centre Aquatic Centre) is a great one for kids. Waterslide, waves, all the fun stuff.

I also recommend you try and get out to Belcarra Regional Park. It has limited bus access or you can drive out there. The Admiralty Point trail as far as Cod Rock is a great little mini-hike to do with 4 year olds and the scenery is beautiful. There is also a fun dock and a new playground. (This is all at the Picnic Area, not the White Pine Beach area, which is also terrific).

In Vancouver the Aquarium would be a hit I think..lots of hands on stuff there..also a ride on the Aquabus to/from Granville Island. if you ride the sksytrain try ot get on the very first car and get the seat at the very front of the train...my husband ( who is a "senior") loves!!! this spot and many "kids" also find it thrilling.

Anther option for getting into Vancouver if you are staying in Coquitlam is to take the Westcost Express train in in the morning..the last train in leaves fairly early (8:10 am) but it's a super way to gt into town...nice train along the water..arrives at Waterfront station by Canada Place at 8:40 am..you could take a bus to Stanley Park from there or take the seabus across Burrard Inlet over to North Vancouver and then take a bus up to Grouse ountain from there

I really appreciate the help folks! I'm printing this page and putting it in my backpack so I won't forget. My son thanks you in advance!