In order for these to connect you’ll need a DUPLO brick or baseplate on top of the System baseplate. Regular LEGO baseplates can accommodate both LEGO and DUPLO. DUPLO obviously won’t stick to regular baseplates as securely as on a DUPLO plate because the studs are much smaller, but they are compatible.
What is a Lego plate?
Plates are very similar to Lego bricks except they are a third of the height of a Lego brick. As well as your standard Lego plates there are many other types of plate. Round Plates allow you to encorporate some curviness into your Lego models. Brackets are handy for attaching parts at right angles.
Are mega blocks made by Lego?
Lego is produced by the Lego Group, a private company in Denmark while Mega Blocks is produced by Mega Brands, a public company based in Canada.