I'm a newly converted muslim I have two children and the man I interested in to get married too is a widower and he has a daughter of three as well muslim - how do I approach him

Before approaching the person in reference, we advise you make Istikhaara
(seek Divine guidance) as well s make Mashwarah (consult) with reliable
people about the person and your intention. If the guidance in the
Istikhaara and Mashwara are positive, then you may appoint a reliable person
as your representative to first enquire from the person if he will be
interested in marrying or not. If he is interested, then he may suggest you
to him.

While it is permissible for a female to make a proposal, we advise the above
procedure of first enquiring and then making an independent suggestion by
your representative due to the misconception that females cannot make a
proposal and is regarded to be incorrect, etc. Should you decide on that
course of action, it is permissible but may not be conducive to your course
due to the misconception of our people.

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai