One in six toddlers in Bath and North East Somerset failed to meet key development milestones last year, new figures show.
A leading children's charity has warned under-resourced services such as family hubs have led to parents being unable to access crucial support.
Office for Health Improvement and Disparities figures show 83% of 1,512 children aged between two and two-and-a-half in Bath and North East Somerset reached the expected standard when they were assessed across five key development areas – up slightly from 82% the year before.
However, this was below 2019-20, the latest data before the coronavirus pandemic, when 86% of toddlers met the expected standard across all five areas.
Across England, the proportion of young children developing as expected remained below pre-pandemic levels, despite rising slightly from 79% to 80%. Before the pandemic, this figure had reached 83%.
Vicky Nevin, policy manager at the NSPCC, said even before the pandemic, too many children were "overlooked".
She added: "It's vital that parents can access trusted advice and support from professionals during this time. However, too often maternity, health visiting and family hubs services are under-resourced and hard to reach for families."
Ms Nevin urged the Government to address the shortages of 2,500 midwives and 5,000 health visitors.
She also highlighted concerning regional inequality, adding: "We need to ensure that children and families across the nation can access quality support – avoiding a postcode lottery.
"We hope to see ambitious commitments on this in the upcoming government spending review and the 10-year health plan."
The figures also showed regional inequality across the country, with children in Yorkshire and The Humber far outperforming their peers in London.
Some 86% of children in Yorkshire and The Humber met the expected standard across all five areas, but this dropped to just 75% for those in London.
In the South West, 81% of toddlers met the expected standard.
Ealing, in the capital, had the worst development rate in England at just 23%, while Wokingham in the South East had the highest at 95%.