Certified GKH Gardening Expert
It is still very early, and it appears that you have a shade cloth over them. They prefer full sun. They are quite a bit more heat tolerant than their cousins, broccoli and cauliflower. If you don't see flowers forming in another month or two, then I would think about adding some phosphorus and potassium to the soil.
Generally, in order for them to flower properly, you will want them quite a bit bigger. Patience will be key here.
This article will give you more information on the subject: https://www.gardeningknowhow.com/edible/vegetables/broccoli/growing-romanesco-broccoli.htm