Is it not illegal to take frogspawn/tadpoles from their habitat, but a few simples rules should be followed.
Ask permission from the person who owns the land where you want to take them from.
Do not take all the frogspawn/tadpoles from the pond/puddle, please leave a large proportion in the pond.
Don't keep them indoors. Preferably keep them in a pond or a shallow container outside so when they turn into frogs they can hop away.
When they do turn into frogs, remember they are wild animals and try not to keep them, let them go if they want to.