Use a centre panel or panel prints, then border it up with fabrics.
This one is smaller than what you want, but gives you the idea.
https://www.flickr.com/photos/87317507@N05/39153818504/
Make a Jumbo block ... as the centre/focal point of the quilt.
Then just extend the quilt size with background fabric.
Works great, if you have larger pieces of fabric for the background.
This is a Radiant Splendour Star that I used when when I needed a quick wedding gift.
https://www.flickr.com/photos/87317507@N05/40710817342/
A Jumbo Churn Dash could work well, with the centre being a kids print or a panel.
The background could be plain or another kids print.
Or a Friendship Star, with each point and the centre in a different colours and/or prints.
Or any sort of a motif in the centre.
Then fill in the background and border as you wish.
https://www.flickr.com/photos/87317507@N05/37578473290/