How to multiply a child dummy variable with its respective ratios in python?

Question

What I want to do is add the ratios in the 1st table based on the correct child in the 2nd table. So for example for the 1st observation I want to do 0.52 (1st child 16-17)+0.84 (2nd child 11-13)+0.78 (3rd child 0-3)=2.14 and create a new column for those values.

There are no observations with more than 1 child in any age range. The "Child_18-older_18" and "Pregnant" columns should be seen as someone with an age of 16-17 and 0-3 in the ratio table, respectively. With regards to the 2nd table, the entire dataframe consists of 4000 observations. These 5 observations were picked randomly

Age	First_child_ratio	Second_child_ratio	Third_child_ratio	Fourth_child_ratio
0-3	1.0	0.72	0.78	0.66
4-6	0.83	0.6	0.65	0.54
7-10	0.77	0.69	0.73	0.59
11-13	0.88	0.84	0.87	0.86
14-15	0.52	0.52	0.68	0.68
16-17	0.52	0.52	0.52	0.52

Pregnant	Child_0-3	Child_4-6	Child_7-10	Child_11-13	Child_14-15	Child_16-17	Child_18-older_18	No_Child
0	1	0	0	1	0	1	0	0
0	1	0	1	0	0	0	0	0
0	0	1	0	1	0	1	1	0
1	0	1	0	0	0	0	0	0
0	0	0	0	0	0	0	0	1