Definitions underlined in bold italics, (Abc)* indicating anagram of Abc,
1 Toy girl? (4)
DOLL. Double definition... and a nod to the phrase "Toy boy".
3 Very good at breaking codes. (8)
CRACKING. Another double definition.
9 Maybe scry unending story with this. (7)
CRYSTAL. [maybe] (scry)* TALe (story) [unending]. Semi&lit.
10 Offspring is a girl. (5)
ISSUE. IS SUE (a girl).
11 PPE put on after a month of lockdown. (5)
APRON. ON [after] APR (April; month of lockdown).
12 Spilt the beans with narrative about king and daughter. (6)
TALKED. TALE (narrative) [about] K (king) [and] D (daughter).
14 Coped nicely with a twice misprinted reference work. (13)
ENCYCLOPAEDIA. (coped nicely... a a)* [misprinted]. Oh dear! As Dashworth0 pointed out in the comments, I have missed an "a" out of the anagrist. Sorry! I need to add "twice", i.e. "...with a twice misprinted...". [Update: crossword and blog updated].
17 Look after these when dieting and the pounds will look after themselves. (6)
OUNCES. Cryptic Definition. With an allusion to the saying "Look after the pennies..."
19 At first the eager novice seemed extremely nervous. (5)
TENSE. Initial letters [at first] of The Eager Novice Seemed Extremely.
22 Picture that is about regular publication. (5).
IMAGE. IE (that is) [about] MAG (regular publication).
23 Somehow very in love, so get engaged. (7)
INVOLVE. [somehow] (v in love)*
24 Tattiest copy is secured in strongbox. (8)
CHEAPEST. APE (copy) inside [is secured in] CHEST (strongbox).
25 Tie up securely with Granny? I hear not. (4)
KNOT. Double definition, 2nd a definition by example, with [I hear] a homophone referring to a Granny knot not being secure.
1 Announced adjusted credit deal without IT. (8)
DECLARED. [adjusted] (credi
2 Put down queen chicken. (5)
LAYER. LAY (put down) ER (queen).
4 Correspondences family member sends overseas. (13)
RELATIONSHIPS. RELATION (family member) SHIPS (sends overseas).
5 Nip in the air leads to infection. (5)
CHILL. Double definition.
6 Rather badly stained. (7)
INSTEAD. [badly] (stained)*
7 Cultivated some meagre wheat. (4)
GREW. Hidden in [some] meaGRE Wheat.
8 Use tech in identifying foreign cultures. (6)
ETHNIC. [use] (tech in)*.
13 Downstairs becomes home for servants over time. (8)
BASEMENT. BASE (home) MEN (servants) [over] T (time). Rememeber Upstairs Downstairs?
15 Boldness about the modern era. (7)
COURAGE. C (about) OUR AGE (the modern era).
16 Ready for operation and liable to erupt. (6)
ACTIVE. Double definition, second as in a volcano.
18 Old Canadian people quietly crawl along the ground. (5)
CREEP. CREE (Old Canadian people) P (quietly).
20 Material found in many long johns. (5)
NYLON. Hidden in [found in] maNY LONg johns,
21 Element unknown in capital of China. (4)
ZINC. Z (unknown) IN [capital (letter) of] China.