Count children from hierarchy path

Question

I have a table like this:

id	name	path
1	John	/1
2	Mark	/2
3	Kevin	/1/3
4	Sarah	/1/3/4
5	Andy	/2/5
...	...	...

So, I can say that Sarah is Kevin's child which is John's child.

I would like to have this:

id	name	path	number of children
1	John	/1	2
2	Mark	/2	1
3	Kevin	/1/3	1
4	Sarah	/1/3/4	0
5	Andy	/2/5	0
...	...	...	...

TASK NUMBER 2: Let's say that I have this table too

id	income	user_id
1	200	1
2	120	1
3	340	2
4	500	3
5	600	5
6	80	5

I can say that John has a Total income of 320$, but if I also want to count John's children, it is 820$ (because id =3 is John's child). So, I would also like a query where I can count all the hierarchical incomes.