You may find this a bit too high-falutin for your tastes, but we used it at ds's baptism, and several people mentioned that they liked it. It's not explicitly about children or babies, but the middle verse in particular is quite appropriate. Rather bizarrely, it's called 'Carol for Advent', but don't let that put you off.
Let love come under your roof:
Oh house him, vagrant;
Happy the eaves where he builds a space-
That light winged migrant.
Italian airs shall echo and hang;
Under each rafter;
He'll touch into silver foil
Your peeling plaster,
Set geraniums round your door,
On hearth lay tinder;
So spead your nets to detain him here-
Don't let him wander.
Love has no manners, and pays no rent,
Full of evasions,
Is rude to your influential friends,
And sneaks the rations;
Sulkily packs his bags and is gone
At your reproof,
Leaving the plaster peeling still,
A leaking roof.
Likely, he'll not be back any more
For tea, nor dinner-
Love is, by nature, impossible-
Learn your dishonour:
Love, Love is a king uncrowned;
In their dumb motion
All the republican stars lament
His abdication.
Once he taught them solfeggios,
Danced in their choirs,
Till intellectual pride untuned
The shining spheres.
If he'd be glad of a share of your board,
Or a place by the fire,
Draw back the bolts, and give up to love
Your easiest chair.
By John Heath-Stubbs
Alternatively, if you can cope with religious stuff, there's the lovely passage in St Marks gospel about 'Let the little children come to me, and do not hinder them.'
dd1 read this at dd2's baptism, which got several people gently dabbing their eyes.
There are actually very few suitable poems, and I did spend quite a lot of time looking. The only other one that springs to mind is the third verse of Coleridge's 'Frost at Midnight' , but it is quite purple, IYSWIM. I think the great poets must have been too busy being creative to really notice their children...