The school holidays are when Bournemouth does what it was built to do, and they are also when it is hardest work. The town does not become unusable — it becomes concentrated, and the difference between a good week and a frustrating one is mostly about where you point yourself.
When it is busiest
The summer holidays through late July and August are the peak, and the Air Festival weekend in late August is the peak of the peak. Half terms and the Easter holidays are busy without being overwhelming.
Accommodation across the whole bay sells out for the Air Festival week. If your dates are fixed and they overlap, book early rather than optimistically.
Where the crowd actually is
Almost entirely within a few hundred metres of Bournemouth Pier, because that is where the car parks, the attractions and the day-trippers all arrive.
The bay is seven miles long. Alum Chine at the western end has a play park at beach level, a café and Blue Flag sand, and holds a fraction of the people. Southbourne at the eastern end is quieter still.
Going early helps as much as going far — the beach before about eleven is a different place.
What works with children
The beach is the default and it is genuinely good for it: continuous sand, gentle shelving, and a promenade that is flat and pushchair-friendly for its whole length.
Beyond that, the Oceanarium sits beside the pier, the Lower Gardens run inland from it, and Boscombe has the watersports for older children who want to be doing something rather than sitting.
Most of what works here is free, which is the underrated argument for a beach holiday.
Eating
Seafront restaurants need booking at weekends through the holidays. Inland is easier and generally better — the independents in Westbourne and Southbourne are the ones residents use, and where locals actually eat covers them.
Rain
It will happen. The indoor options cluster near the pier — the Oceanarium, the Russell-Cotes museum, the cinemas and covered shopping in the town centre.
Related
Bournemouth with kids for a week covers pacing a longer family stay, and when to go sets the holiday periods against the rest of the year.