So you your child has just finished Y1? As an ex-teacher with still-teaching friends, a lot of them say the cohort that has just finished Y1 have really struggled in general since starting school - they were at most 2.5yrs when COVID and lockdowns began, and they missed a good chunk of the socialisation and 'soft skill building' that toddlers do at playgroups/preschool etc.
(One teacher friend said her Y1 class was almost feral when they started - had little idea how to use the classroom equipment, let alone listen to anyone - and they had been in YR by then too)
I have a nephew in said cohort (just finished Y1) who has intelligent parents but is 'working towards' in all areas. However, his report comments on how friendly, helpful, and empathetic he is, how he is quick to invite others to play and join in, and how he manages his own friendships by talking and trying to solve problems. This is all far more important at 6 than the fact he is below what the National Curriculum deems 'average' - that will come. Or it won't, in which case support will be sought as required.
By contrast, his 10 year old brother (just finished Y5) is 'average' in all areas (but still great comments on his behaviour/temperament/interaction with others), when actually he's quite capable of much more and coasts along doing the bare minimum. We suspect he will come into his own at secondary school when it's more interesting to him.
It might seem unusual to have a 'below average child' if both parents are high achievers (although as others have pointed out - high achiever does not always equal highly intelligent), but things tend to even themselves out ultimately.