You’ll want to accomplish this using CSS.
Decide on the proportions you want. For instance, the large could be 28% while all the small ones could be 12% width each.
28 + 12*6 = 100.
In your styles.css
in the assets folder, simply add
.big-card {
width: 28%
}
.small-card {
width: 12%
}
On each card, just add the appropriate classname.
big_card = dbc.Card(children, class_name='big-card')
small_card = dbc.Card(children, class_name='small-card')