Are you actually wanting them to
visit Europe? Or are you wanting to live in Europe with you? And indeed live with you in the Netherlands?
If so, yes get married in Kenya, when safe to do so, then as you say apply at the Dutch embassy in Kenya.
Transit via the UK? Kenyans are subject to the DATV .. direct airside transit visa ..... requirements, so at first glance a DATV visa would also be required from the British Embassy if the flight is going to be via the UK ..... except :-
It looks like the Dutch visa would be one of the following :-
- a valid common format Category D visa for entry to a European Economic Area (EEA) State;
- a valid common format residence permit issued by an EEA State pursuant to Council Regulation (EC) No. 1030/2002
-: in which case, once the Dutch-issued visa is in the passport, there would be no requirement for a UK-issued DATV. So flight via the UK would be OK. But do appreciate that they would need to remain airside, and not allowed to enter the UK as such.
Actually, your child? Has the child got a British Passport? Are you named as the father on the birth certificate?
Marriage of convenience? I think the existence of the child proves otherwise. But don't skimp on the supporting evidence to show the relationship is real.