This is what we made:
Cardboard box aquarium
Paint - green, blue and sand coloured
Glue (we used Bostik blu stick)
Small under the sea themed toys
Cotton and needle
Cut the top and side flaps off the cardboard box. Make sure that all the inside flaps are either removed or stuck down securely - we used double sided tape but I actually ended up having to sew it closed with a few stitches as the cardboard warped when it was painted. Mark out lines down the sides for the sandy section of the box, then paint blue and sand coloured.
When the paint has dried, use a sponge and the green paint to make seaweed.
When this layer of paint is dry, cover the inside of the box with glue and sprinkle on blue glitter. To stick the glitter we used the Bostik blu stick. We get through glue sticks at an astonishing rate, but this one was particularly good because when you first apply it the glue shows blue, then it dries clear, so you can see where you've put it. Great for crafting with little ones that tend to apply liberally, as they can see where they have already put the glue.
Then you can use fish stickers to decorate the inside of the box. I also hung a couple of the large foam fish stickers from the top of the box with a length of cotton so that they can dangle inside. We finished off our under the sea scene with some shells glued to the bottom of the box, some treasure and a diver figure.
Under the sea viewer
Shallow lid from a shoebox
Craft knife and cutting board
Small fish stickers
Use the craft knife to cut a window out of the box lid. It doesn't matter if the sides are a bit wavy, that adds to the underwater effect! Stick a sheet of cellophane across the window and secure at the sides with tape. Stick some fish stickers over the window.
Explore the house looking through the underwater viewer, making the fish swim across the furniture! The children played for ages with this, with all sorts of under the sea role play!
The box of craft materials was provided to me free of charge by Bostik as part of the Tots100/Bostik Craft Bloggers Club.