I googled 'northern virginia tea party event planner' (minus the quotes) and got at least 10 results. Similar for DC or Maryland. Looks like some can accommodate kids and will come to you. Went to one of these for a friend's 50th birthday where they brought all the tea, sandwiches, cookies, cups, etc. and it was really nice.
Probably not what you were looking for but also found this great site which lists the places that offer tea service by state: https://destinationtea.com/

What's the planned number to attend, and what is your budget for someone to do this?

I once attended a preschool tea party where an outside party decorated and hosted the most adorable tea party. I tried to find the invitation but it must have been a paper invitation. Yes, some people still used those.

Can you recommend a party planner who could do this for us?