Spanish eyes
I think, if anything, Jet2 are just being realisitc with the likely slow opening of borders. The case rate in many parts of Europe is sky-high compared to here. The government here are obviously going very slowly in comparison to the big bang opening we saw last summer.
It depends on your definition of child, but the Pfizer vaccine is licensed for those aged 16 and above. They've completed the trial for kids aged 12-15 and submitted that for approval to the FDA in the US. I imagine they'll do the same here in the near future.