Firstly, it's just a proposal for the party to discuss, so the "Jeremy Corbyn wants to impose..." bit is ridiculous.
Secondly, even if it was agreed upon, which it likely wouldn't be, it'd be in amongst all the other policies.
So, while your child potentially wouldn't be able to receive more than £125k as a gift, your child also would have free university tuition or training, and access to the NHS, which ARE Labour policies. They'd grow up in a society which was a bit more supportive, where there was more funding in housing, in healthcare, in social services, so it'd be likely to have lower crime. They'd be likely to have higher wages when starting out.
On the other hand, if the Conservatives stay in then children will probably need as much gift money as possible, as the NHS gets more and more privatised, services are cut, communities fall apart with lack of infrastructure and transport, and a few people get richer and richer.