There's a public tree on Ancestry which states that Timothy Sherwin Brook was indeed the son of James and Mary and that he was baptised 27/12/1791 at St. Stephens, Ipswich. It also shows 5 siblings but no actual baptisms for any of them:
Mary Ann 1787
Elizabeth 1789
James Blyth 1790
Timothy Serwin bp.27/12/1791 St. Stephens, Ipswich
Lucy 1795
Annette