Why don't we just say they're each 1HD, Small, and have 1 tentacle? Then the DM can "deadvance" them as needed.
I was going to make them 1 HD Tiny, following the usual halve HD per size step smaller, and give them two tentacle attacks.
Something like:
Baby Rekeihs
Tiny Plant
Hit Dice: 1d8+1 (5 hp)
Initiative: +1
Speed: 10 ft. (2 squares)
Armor Class: 15 (+2 size, +1 Dex, +2 natural), touch 13, flat-footed 14
Base Attack/Grapple: +0/-9
Attack: Tentacle +1 melee (1d4-1)
Full Attack: 2 tentacles +1 melee (1d4-1)
Space/Reach: 2.5 ft./0 ft
Special Attacks: —
Special Qualities: All-around vision, darkvision 60 ft., low-light vision, myopic, plant traits, resistance to cold 10, vulnerability to fire
Saves: Fort +3, Ref +1, Will +1
Abilities: Str 8, Dex 13, Con 12, Int 3, Wis 12, Cha 9
Skills: Listen +5
Feats: Improved Disarm (B), 1 more
Challenge Rating: 1/10
Although that is rather wimpy, so maybe making them Small would be better...
Baby Rekeihs
Small Plant
Hit Dice: 1d8+2 (6 hp)
Initiative: +0
Speed: 10 ft. (2 squares)
Armor Class: 15 (+1 size, +4 natural), touch 11, flat-footed 15
Base Attack/Grapple: +0/-3
Attack: Tentacle +2 melee (1d6+1)
Full Attack: 2 tentacles +2 melee (1d6+1)
Space/Reach: 5 ft./5 ft
Special Attacks: —
Special Qualities: All-around vision, darkvision 60 ft., low-light vision, myopic, plant traits, resistance to cold 10, vulnerability to fire
Saves: Fort +4, Ref +0, Will +1
Abilities: Str 12, Dex 11, Con 14, Int 3, Wis 12, Cha 9
Skills: Listen +5
Feats: Improved Disarm (B), 1 more
Challenge Rating: 1/3
Do you agree with combining the "raise dead time limit" and the explosion time?
I prefer the far shorter
raise dead time limit.