The hardest part of buying for a child you don't parent is that you're guessing at an age band. Under ₹500 the safest hedge is something with no age gate at all — the Parssufy art set and the Mikado sticks both work from about five upward, and neither needs a rulebook explained by a stranger. Save the specific stuff for children you actually know.
If the party is the venue, favour things that work for a group. Ratna's 5-in-1 box plays two to four and holds five different games, so an afternoon that runs long has somewhere to go. Strike 4 is the opposite trade: two players only, but the rules land in one sentence, which makes it the right thing to leave with a child and a grandparent.
On the two remote-control cars, read the battery line before you decide. The NHR ships with a rechargeable pack and a USB charger, so it works the moment it's unwrapped. The Gooyo is cheaper and comes in gift-box packaging, but it needs five AA cells that aren't in the box — a detail that turns a birthday present into an anticlimax if nobody checked. Buy the batteries at the same time or buy the NHR.
One honest caveat across the whole list: prices at this end move, and stock on cheap toy listings moves faster. Check the live price before you commit, and if a pick is gone, the nearest equivalent on this page is usually the better choice over a lookalike from an unfamiliar seller.