Presumably his wife has planned another pregnancy and they are excited to be expecting a baby later in the year. For all my personal disbelief that any woman, let alone several, want to have sex with Boris Johnson, there are many more things going on that occupy my thoughts.
Yes, he has several children already and I’ve no idea what type of relationship he has with them or how involved he is as a parent but I can’t believe this baby is anything other than wanted and wished for.