Vaheguru Ji Ka Khalsa! Vaheguru Ji Ki Fateh!
Veer Ji, from my limited understanding, it's always best to do Seva ourselves. Additionally, I think that Guru Sahib Ji has SO many Rumalla Sahibs that are given as Seva. From what I understand, it would be much better to go to Gurdwara and do Seva - Jorreh (Shoe) Seva, Charru Seva, washing dishes, helping to prepare langar, etc. Also, making a habit of doing this Seva as much as you can, would be ideal. For those of us who do seva for a purpose (like obtaining a child), it doesn't always happen after one time of Seva. Sometimes certain things are written for us and through Seva, Naam, Bani, these things can change.
Furthermore, it may be better to use the money instead to help Gareeb lok pay for school fees, necessary medical operations, food, clothes, etc. Guru Ji has said that "Gareeb Da Mooh, Guru Da Golak Hai." In fact, our Guru Sahiban have history of advising their Sikhs and wives to do the same (giving to lorrh-van) when having trouble with conceiving a child. For more information on what Sikhs and Guru's own wives were told to do for children, see the links above for
www.sikhfamilylife.comAdditionally, are you and your wife doing any separate paath for a child? Doing whatever you can, in addition to your Nitnem, would also be helpful, followed by an ardaas asking for Guru Sahib Jee to send you a Gursikh child.
The latest post, Maa De Farz Part 8 that's coming out this Friday (August 31, 2018) may also address this issue of the blessing of a child and may be of interest to you.
Bhul Chukk Maaf Kardo Ji, if I've said anything wrong.
Vaheguru Ji Ka Khalsa!
Vaheguru Ji Ki Fateh!