Ok...let's break this down and keep it in context.
Rev. 5:8, Rev. 8:3–4.
Jesus himself warned us not to offend small children, because their guardian angels have guaranteed intercessory access to the Father: "See that you do not despise one of these little ones; for I tell you that in heaven their angels always see the face of my Father who is in heaven" (Matt. 18:10).
Mary is not an angel. Angels are separate created beings and are not people so trying to apply this verse to justify praying to Mary fails. Secondly, we're not talking about children....we're talking about grown adults. In either case we are not to pray to angels anymore than we are to pray to Mary. Our prayers should be directed to Christ.
Because he is the only God-man and the Mediator of the New Covenant, Jesus is the only mediator between man and God (1 Tim. 2:5),
and as such we should only pray to Him. There is no need for mary to "intervene" in our salvation or any of the other things catholicism claims she does.
Why would the catholic want to replace, or probably in their worldview, supplement, what Jesus is doing for us? Is the Second Person of the Trinity, Who was, is and is to come again, Who has always existed, Who created all we know, Who died on the cross for us, in some way deficient??
In the catholic worldview Mary is replacing Jesus in this capacity with all of the prayers to her for her intercession in the affairs of man. This is where the fifth marian dogma, if passed, will elevate mary officially to the position of mediatrix; that is currently what Jesus does for us. To imply that Mary's help is needed undermines the full confidence we are to have in Jesus. Only one person I can think of would want that to happen. His name is Satan.
but this in no way means we cannot or should not ask our fellow Christians to pray with us and for us (1 Tim. 2:1–4).
On this there is no agreement....however from the conversation we've been enjoying, the fundamental difference is that Christians do not pray to our fellow Christians....we pray with them. Catholicism prays to mary and the saints who've gone on before us.
Nor do we rely upon them for our salvation or "place our hopes" in them nor devote ourselves fully to them as the catholic does when they pray to mary and adhere to the belief she is taking an active role in our salvation and even, according to some catholic writers, "tells" Jesus to save some and He then acts.
In particular, we should ask the intercession of those Christians in heaven, who have already had their sanctification completed, for "[t]he prayer of a righteous man has great power in its effects" (Jas. 5:16).
There is no indication that James was suggesting we pray to believers who have gone on to Heaven.
For the verses in Revelation regarding the saints assumes 1)that they are able to hear our prayers, which there isn't any Biblical indication to suggest they can, or 2) but assume they can, again we are not shown to pray to fellow believers in any capacity.
The prayers of the saints noted in Revelation appear to be those believers who are already in Heaven and who will be in Heaven. Revelation 6:9 strongly suggests they are saints who were killed for their faith and have gone to Heaven. So the two passages you referenced, 5:8, Rev. 8:3–4 more than likely refer to them.
Regardless of their status, we are not to pray to them, nor is there a Biblical injunction to pray to those who've gone on before us.
Let's not forget the role of the Holy Spirit in the life of the believer still on earth. He is constantly interceding for us with words and groanings we cannot understand. He is our Advocate and Helper. And if the fifth marian dogma is passed, He will be "replaced" by mary in this capacity.
And this takes us back to the whole problem with the catholic position on mary. Slowly but surely the rcc is elevating mary to positions of authority which are not granted to her by the Word.
This is why Christians reject catholic tradition. It leads to such false teaching as what we see on mary and what is being proposed for mary.
So, when your friends, or even strangers, ask you to pray for them, you refuse and tell them to go directly to Jesus.