No. Czech numbers (including words that define amounts like many, a lot, few, several...) are weird.
2, 3 and 4 are followed by nominative and would have JSOU
5 and everything higher, including undefined amounts are followed by genitiv and JE
What I mean with the nominative and genitive
3 děti jsou modré.
6 dětí je modrých
mnoho dětí je modrých
The TIPS for numbers are on the list of Tips next, so hopefully the explanation there will be little more "scientific"....