Cheapest way to get kids sim

Bexm

Hi

My son is really too young for a mobile yet, but we've set him up a hyper jar/go Henry type card and to access the kids app he needs to have a mobile number to register it against on a phone.
Both my husband and I already have the app so we can't use our phones so we need a way of getting a separate phone number.
What's the absolute cheapest and long lasting way to do this?
Back in the day pay as you go Sims could be topped up once and the credit lasted forever but I know that's not true anymore and I'm having trouble finding information on how often you need to top up on various providers.
Can anyone help? 

molerat

What does the sim need to do ?  If it is just to register and receive text messages then surely any free sim will do.  MrsM has one in her tablet that has never been used, had it 18 mths, but still receives the odd text message I send.

Bexm

@molerat What network is that?
I keep seeing ones where they say if you don't top them up every month or so they disconnect? 

flaneurs_lobster

Asda mobile, £5 minimum credit, never expires, need to make 1 charged call/send 1 charged text every 180 days to keep it active (costs 4p). Sim is free to get online or 50p in Asda.

PaulStev0

When he is ready for a phone, the remote parental controls provided with the ParentShield mobile network may be of interest 

531063

RWG mobile