preallocate new children array (#4595) #4173

Job	Run time
Filter jobs	5s
Build & Test / Build & Test	1m 10s
Compressed Size / build	53s
Benchmarks / Prepare environment	4s
Benchmarks / Bench create10k / Bench table-app/create10k	2m 39s
Benchmarks / Bench many-updates / Bench many-updates/many-updates	2m 3s
Benchmarks / Bench filter-list / Bench filter-list/filter-list	1m 26s
Benchmarks / Bench hydrate1k / Bench table-app/hydrate1k	1m 57s
Benchmarks / Bench replace1k / Bench table-app/replace1k	3m 5s
Benchmarks / Bench text-update / Bench text-update/text-update	1m 58s
Benchmarks / Bench todo / Bench todo/todo	1m 40s
Benchmarks / Bench 03_update10th1k_x16 / Bench table-app/update10th1k	1m 21s
	18m 21s

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